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Sacramento River

The Sacramento River is an important river of Northern and Central California in the United States. The state's largest river by discharge, it rises in the Klamath Mountains and flows south for over before reaching Suisun Bay, an arm of San Francisco Bay, and thence the Pacific Ocean. The Sacramento drains an area of about in the northern half of the state, mostly within a region bounded by the Coast Ranges and Sierra Nevada known as the Sacramento Valley. Its extensive watershed also reaches to the volcanic plateaus of Northeastern California. Historically, its watershed has reached farther, as far north as south-central Oregon where the now, primarily, endorheic (closed) Goose Lake rarely experiences southerly outflow into the Pit River, the most northerly tributary of the Sacramento.

The Sacramento has been an important transportation route since the time of the region's first inhabitants, who settled in the river valley about 12,000 years ago. Hundreds of tribes sharing regional customs and traditions inhabited the Sacramento Valley, though they received little disturbance upon the arrival of Europeans in the 1700s. One of these early explorers, Gabriel Moraga, gave the river the Spanish name, Rio de los Sacramentos, later shortened and anglicized into Sacramento. The Sacramento's waters were once abundant in fish and other aquatic creatures, notably one of the southernmost runs of chinook salmon in North America. The original natives of the Sacramento Valley drew upon the vast natural resources of the watershed, which had one of the densest American Indian populations of California.

In the 19th century the discovery of gold in the Sierra Nevada led to an enormous population influx of American settlers. Overland trails such as the California Trail and Siskiyou Trail followed the Sacramento and other tributaries, guiding hundreds of thousands of people to the goldfields and the growing agricultural region of the Sacramento Valley. By the late part of the century, many populated communities had been established along the Sacramento River, chief of which was the booming city of Sacramento. Intensive agriculture and mining contributed to pollution in the Sacramento, and significant changes to the river's hydrology and environment.

Since the 1950s the watershed have been intensely developed for water supply and the generation of hydroelectric power. Today, large dams impound the river and almost all of its major tributaries. The Sacramento's water is used heavily for irrigation purposes and serves much of Central and Southern California through the canals of giant federal water projects. While now providing water to over half of California's population and supporting one of the most productive agricultural areas in the nation, these changes have left the Sacramento greatly modified from its natural state and have caused the decline of its once-abundant fisheries.



The Sacramento's source waters rise in the volcanic plateaus and ranges of far northern California as two streams the Upper Sacramento and Pit. The main stem rises in the shadow of Mount Shasta and flows south through the Klamath Mountains, past Mount Shasta, Dunsmuir and Lakehead for about . However, the river's true headwaters lie far to the northeast, as the Pit River, which is formed by streams flowing southwest from the Modoc Plateau. The two rivers join in the waters of Lake Shasta, a giant reservoir formed by the Shasta Dam.[1] The upper Sacramento is only the main stem by name: the flow of the Pit into the lake, ,[2] is nearly four times that of the Sacramento's .[3]

From the dam the Sacramento winds south through foothills and leaves the mountains near Redding, the first larger city on the river's course and second largest on its entire course. Many small and moderate-sized tributaries join the river from both east and west including Clear, Cottonwood, Cow, Thomes, Ash and Battle Creeks. As the river meanders into the Central Valley a large portion of its flow is diverted into a pair of irrigation canals at Red Bluff. The Sacramento continues south, receiving Mill Creek near Tehama, and Stony and Big Chico creeks a bit southwest of Chico. The river then passes Colusa, and receives Butte Creek about west of the Sutter Buttes, a group of isolated volcanic hills in the middle of the Sacramento Valley.[1]

Twenty-five miles (40 km) southeast of Colusa near Fremont Landing, the Sacramento incorporates the flow of its largest tributary, the Feather River, which descends from the Sierra Nevada to the northeast. About downstream, it flows into the city of Sacramento, California and receives the American River, its second largest tributary. Here the river splits into two: the main stem and the artificial Sacramento Deep Water Ship Channel. Both waterways continue south through the lowlands, eventually to rejoin in the estuary of the Sacramento-San Joaquin Delta near Rio Vista.[1]

The mouth of the Sacramento is on Suisun Bay near Antioch, where it combines with the San Joaquin River, south of the Montezuma Hills. The Sacramento is nearly a mile (2 km) wide at its mouth. The joined waters then flow west through the tidal marshes of Suisun Bay, the Carquinez Strait, San Pablo Bay and San Francisco Bay, whereupon the river's waters finally join the Pacific in the Golden Gate just to the north of San Francisco.[1]


The Sacramento River's average annual discharge is about , carrying over of water each year, making it the second largest river on the Pacific coast of the continental United States.[4] The U.S. Geological Survey has stream gauges on several locations along the Sacramento River. The ones currently in operation are at Delta (near the source at Mount Shasta), at Keswick (near Redding), Colusa (about halfway down the river), Verona, and Freeport. At the Delta gauge, which began operation in 1945, the average annual discharge was .[3] At Keswick, after receiving major tributaries such as the Pit, the river's flow increases to .[5] The Colusa gauge recorded an annual mean of from 1946 to 2009.[6] At Verona, downstream from the Feather River confluence, the Sacramento's flow rises to .[7] The final gauge, at Freeport, sits just downstream of Sacramento; it recorded an average flow of from 1949 to 2009.[8] The USGS also operates many other gauges, including at Sacramento and Rio Vista, but the data recorded at these stations is more spotty.[9]

Sacramento River monthly discharges at Freeport (cfs)[10] Colors= id:lightgrey value:gray(0.8) id:darkgrey value:gray(0.3) id:sfondo value:rgb(1,1,1) id:barra value:rgb(0.6,0.8,0.9)

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The Castle Crags, a series of granite peaks rising above the upper Sacramento River canyon just to the right. Mount Shasta, the highest mountain in the Sacramento drainage, is seen in the distance.
The Castle Crags, a series of granite peaks rising above the upper Sacramento River canyon just to the right. Mount Shasta, the highest mountain in the Sacramento drainage, is seen in the distance.
The largest river in California, the Sacramento River's watershed covers a a large portion of the northern portion of the state and is situated almost entirely within California's boundaries, with the historically rare exception of the northernmost Pit River, which once received outflow of the now endorheic (closed) Goose Lake drainage basin in southern Oregon. Almost the entire basin lies between the Sierra Nevada and Cascade Range on the east and the Coast Ranges and Klamath Mountains in the west.[11] The Sacramento's longest tributary, the Pit River, has the distinction of being one of three rivers that cut through the main crest of the Cascades; its headstreams rise on the western extreme of the Basin and Range Province, east of major Cascade volcanoes such as Mount Shasta and Lassen Peak. The other two are the Klamath River and Columbia River.[4][12]

By discharge, it is the second-largest contiguous U.S. river draining into the Pacific, after only the Columbia River, which has almost seven times the flow of the Sacramento. The Colorado River, which reaches the Gulf of California just south of the US-Mexico border near the southeast part of the state, is far larger than the Sacramento by both length and drainage area but has a slightly smaller flow.[13] After the Colorado and San Joaquin, it has the third-largest drainage basin in California. The Sacramento, when combined with the Pit, is also one of the longest rivers in the United States entirely within one state—after Alaska's Kuskokwim and Texas' Trinity.

The major drainage basins bordering that of the Sacramento are that of the Klamath in the north, the San Joaquin and Mokelumne to the south and the Eel River in the west. The Russian River also lies to the west and the endorheic (closed) Honey Lake and Eagle Lake basins to the north. On the east side are many endorheic watersheds of the Great Basin including the Truckee River and Carson River. Parts of the Sacramento watershed come very close to, but do not extend past, the border of California and Nevada.[14][15]

The basin's diverse geography ranges from the glacier-carved, snowcapped peaks of the Sierra Nevada to the sea-level (and often lower) marshes and agricultural lands of the Sacramento-San Joaquin Delta. The highest point is Mount Shasta, a stratovolcano that stands high, near the headwaters of the Sacramento River.[16] Subsidence caused by wind erosion and other phenomena slowly caused the land in the delta to sink for years; many of the delta islands would be underwater if not for the maintenance of the levees that keep them dry. Many of the "islands" are now up to below the surrounding water.[17] The Sierra Nevada generally decreases in height from south to north—from near Lake Tahoe, east of the American River, to just as they merge into the Cascades and Modoc Plateau in the Lassen Peak area; however, on the west side, the Coast Ranges area is the opposite, increasing from in the south to just shy of in the north. The volcanic plateaus in the northeast, which comprise relatively flat terrain, typically lie at elevations of . Most of the Sacramento Valley is below in elevation; in its lower course, the Sacramento River drops only about per mile.[1][18]

Most of the Sacramento River's valley is intensely cultivated, with some of irrigated farmland. Medium to dense forests occupy most of the mountains, many of which lie on U.S. Forest Service lands. Sparse grasslands and high desert stretch to the north. Along with the agrarian base, the basin is also home to about 2.8 million people, far more than half of whom live within the Sacramento metropolitan area.[19] Other important cities are Chico, Redding, Davis and Woodland. The Sacramento River watershed covers all or most of Shasta, Tehama, Glenn, Butte, Plumas, Yuba, Sutter, Lake and Yolo Counties. It also extends into portions of Siskiyou, Modoc, Lassen, Lake (in Oregon), Sierra, Nevada, Placer, El Dorado, Sacramento, Solano and Contra Costa Counties. The river itself flows through Siskiyou, Shasta, Tehama, Butte, Glenn, Colusa, Sutter, Yolo, Sacramento, Solano and Contra Costa, often forming boundaries between the counties.[11]

The Sacramento River watershed includes large areas of forests such as the Mendocino and Trinity National Forests in the Coast Ranges, Shasta and Lassen National Forests in the southern Cascades and the Plumas, Tahoe and Eldorado National Forests on the western slopes of the Sierra Nevada. The watershed also has Lassen Volcanic National Park, which covers centered around Lassen Peak, the southernmost Cascade volcano.[20] Whiskeytown-Shasta-Trinity National Recreation Area, which is over in size, straddles much of the upper Sacramento and Trinity Rivers, centering around three popular man-made lakes Shasta Lake, Trinity Lake and Whiskeytown Lake. Many other state parks and recreation areas lie within the watershed.[1]


The Carquinez Strait, which connects the Sacramento-San Joaquin Delta and Suisun Bay to San Pablo and San Francisco Bays then the Pacific. The channel formed from water flooding over the Coast Ranges from a gigantic lake that formed in the Central Valley a few hundred thousand years ago, when the rising mountains blocked the Sacramento's route to the Pacific Ocean.
The Carquinez Strait, which connects the Sacramento-San Joaquin Delta and Suisun Bay to San Pablo and San Francisco Bays then the Pacific. The channel formed from water flooding over the Coast Ranges from a gigantic lake that formed in the Central Valley a few hundred thousand years ago, when the rising mountains blocked the Sacramento's route to the Pacific Ocean.
By geologic standards, the Sacramento is a fairly young river; the borders of its watershed began to form only a few million years ago as magma welling up below the Earth's crust pushed up by the Pacific Plate colliding with the North American Plate caused the formation of the Sierra Nevada. Although mountains had existed as early as 100 million years ago in this region (before then the land was probably submerged under the Pacific), they were worn by erosion, and the present-day range only formed about 4 million years ago.[21] The northern part of the Sacramento watershed is more ancient, and was formed by intense volcanic activity over 25 million years ago, resulting in lava flows that covered and created the Modoc Plateau, through which the Pit River flows. Mount Shasta and Lassen Peak are among the numerous Cascade Range volcanoes that still stand in the area.[22]

As the Sierra rose, the ancestors of the Sacramento's east side tributaries and numerous glaciations carved deep canyons in the mountains, depositing massive amounts of silt between the Sierra Nevada and the Pacific, slowly building up the floor of the Sacramento Valley. The Sacramento River did not form until multiple terranes were formed and smashed into the North American Plate from the Pacific Plate about 3 million years ago. The resulting geologic folding pushed up the California Coast Ranges and Klamath Mountains, enclosing the Sacramento Valley and forcing the streams within to flow south instead of west and forming the ancestral Sacramento River. It is believed that the river once had its outlet in Monterey Bay (forming the Monterey Submarine Canyon when sea levels were lower during the Ice Ages). While the Coast Ranges are young by geologic standards, only a few million years old, the Klamath Mountains reached their present form some 7.5 million years ago.[23][24]

The Monterey Bay outlet of the Sacramento and San Joaquin rivers was blocked off about 2 million years ago, and runoff from the Sierra began to transform the Central Valley into a gigantic lake, called Lake Clyde. This lake stretched north to south and was at least deep. About 650,000 years ago the lake catastrophically overflowed, draining into San Francisco Bay and creating the Carquinez Strait, the only major break for hundreds of miles in the Coast Ranges.[25] The narrow outlet trapped some of the sediments of the rivers in the Central Valley, forming the Sacramento-San Joaquin Delta. For thousands of years, this inland sea would periodically reform during times of intense flooding, the most recent being the Great Flood of 1862. Dams and canals that control the river now prevent this phenomenon from occurring in most years.[26][27]


The Sacramento River and its valley were one of the major American Indian population centers of California. The river's abundant flow and the valley's fertile soil and mild climate ensured enough resources for hundreds of groups to share the land. Most of the villages were small. Although it was once commonly believed that the original natives lived as tribes, they actually lived as bands, or family groups as small as twenty to thirty people.[28] The Sacramento Valley was first settled about 12,000 years ago, but permanent villages were not established until about 8,000 years ago.[29] Historians have organized the numerous separate original native groups into several "tribes". These are known as the Shasta, Modoc, and Achomawi/Pit River Tribes of the volcanic plateaus in the north; the Wintu and Hupa in the northern Klamath and Trinity mountains; the Nomlaki, Yuki, Patwin, and Pomo of the Coast Ranges; the Yana, Atsugewi, Maidu, Konkow, and Nisenan in the Sierra and their western foothills; and the Miwok in the south.[30][31]

Life for Native Americans in the Sacramento Valley was relatively simple and involved little violence. Little agriculture was practiced; most were hunter-gatherers and fishermen. Settlement size ranged from small camps to villages of 30 50 permanent structures.[32] As with tribes in the San Joaquin Valley and throughout much of California, the acorn was a staple food. The historic abundance of white oaks in the Sacramento Valley was capable of supporting a large population. American Indians usually pounded the acorns into flour, which they used to make bread and cakes. Despite the prevalence of acorns in their diet, they also consumed a variety of other foods—wild roots, seeds, berries, and game that included fish, deer, rabbits, and birds.[33] The natural abundance of the Sacramento River and its valley, along with the San Joaquin, probably once supported most of California's original 275,000 300,000 Native Americans.[34]

The Sacramento-San Joaquin Delta viewed from Mount Diablo, near where Fages and his crew are believed to have first caught sight of the Sacramento River
The Sacramento-San Joaquin Delta viewed from Mount Diablo, near where Fages and his crew are believed to have first caught sight of the Sacramento River
The first outsiders to see the river were probably the members of a Spanish colonial-exploratory venture to Northern California in 1772, led by Captain Pedro Fages. The group ascended a mountain, likely in the hills north of Suisun Bay, and found themselves looking down at the delta of the Sacramento and San Joaquin Rivers. However, due to their vantage point, neither Fages nor any of his men saw the Sacramento clearly. They assumed that the San Joaquin, coming from the south, was the largest of the merging rivers they saw. In 1808, explorer Gabriel Moraga, on a journey to find suitable sites for the construction of missions, became the first foreigner to see the river clearly. Judging its huge breadth and power he named it Rio de los Sacramentos, or "River of the Blessed Sacrament". In the following years, two more Spanish expeditions traversed the lower part of the river, the last one in 1817.[35][36]

The next visitors were Hudson's Bay Company (HBC) fur trappers exploring southwards from the disputed Oregon Country, starting in the 1820s. The first organized expedition, led by Peter Skene Ogden, arrived in the area of Mount Shasta in 1826.[37] By this time, California was under the control of Mexico, although few Mexican settlers had come to what would later become the state, mostly settling in the small pueblos and ranchos along the south and central coast. The HBC mountain men created the Siskiyou Trail out of several Native American paths that ran through the mountains between Oregon's Willamette Valley and the northern part of the Sacramento Valley. In the years to come, this path, which eventually extended from San Francisco to Portland, Oregon following parts of the Sacramento, Willamette, Klamath, Rogue, and other rivers would become an important trade and travel route.[37][38]

Although just one of thousands of American emigrants that poured into California over the next few years when California became part of the United States, John Augustus Sutter became one of the most significant settlers of the Sacramento River valley. In 1841, he and his men built a fortress at the confluence of the Sacramento and American Rivers (the latter of which was actually named by him) and he was granted almost of land surrounding the two rivers. Naming it New Helvetia, he created an agricultural empire in the lower Sacramento Valley, attracting hundreds of settlers to the area, and relied on Native American labor to maintain his domain. Sutter had something of a two-faced relationship with the many Native American groups in the area. He was friendly with some of the tribes, and paid their leaders handsomely for supplying workers, but others he seized by force and made them labor in his fields.[39][40][41]

Chrysopolis, one of several large steamboats that served for transportation on the river during the California Gold Rush
Chrysopolis, one of several large steamboats that served for transportation on the river during the California Gold Rush
Sutter's prosperity, however, indirectly led to his financial demise, and the rise of one of the most significant events in California history. When one of his employees, James W. Marshall was assigned to build a sawmill on the South Fork American River in Sutter's interests, he discovered gold in the headrace.[42] It was not long before the secret slipped out attracting three hundred thousand hopefuls from all over North America, and even the world, to the Sacramento River in search of fortunes, kicking off the California Gold Rush.[43] People flocked to the region by the Oregon Trail-Siskiyou Trail, California Trail, Southern Immigrant Trail and various land and/or sea routes through the Isthmus of Panama and around southern South America by ship. Steamboats traveled busily up and down the Sacramento River carrying miners from San Francisco to the "gold fields".[44] As the miners expanded their diggings deeper into the Sierra Nevada and Klamath Mountains, Native Americans were pushed off their land and a long series of skirmishes and fights began that continued until intervention by the state and national governments.[45]

The influx of migrants brought foreign diseases like malaria and smallpox, which American Indians had no immunity to. These diseases killed off a large proportion of their population within a few decades of the arrival of Sutter and the following settlers,[46][47] the start of the gold rush, not to mention the numerous battles fought between the settlers and native bands as well as the forced relocation of some of the tribes to Indian reservations in several places scattered around the Sacramento Valley, mainly in the Coast Ranges.[48] In the early 1850s, several treaties were signed between the U.S. government and the Native Americans involving their relocation onto a reservation in the Sierra foothills; this promise was broken, of course. Therefore in 1863, the tribes from the area surrounding the middle Sacramento and Feather rivers, the Konkow group, were removed and marched forcibly to the Round Valley Indian Reservation near the Eel River. A total of 461 people were forced from their homes, but only 277 made it to the reservation before dying of disease, starvation or exhaustion.[49][50]

As mining developed from simple methods such as panning and sluicing to a new form of commercialized extraction, hydraulic mining, profits from the petering gold rush made a second leap, earning more profits than those miners in the early years had ever made.[51] The city of Sacramento, founded on the original site of Sutter's fort, began to flourish as the center of an agricultural empire that provided food to feed the thousands of miners working in the hills as well as a place of financial exchange of all the gold that was mined. Sacramento was officially established in 1850 and was recognized as the state capital in 1854.[52] As the economy of the Sacramento Valley grew, the Southern Pacific Railroad established tracks along the river to connect California with Oregon following the ancient path of the Siskiyou Trail, in the 1880s and 1890s.[53] Many parts of the railroad were treacherous, especially in the mountainous areas north of Dunsmuir.[54] It was not long after the city had reached a relatively large population of about 10,000, then the Great Flood of 1862 swept away much of it (and almost everything else along the Sacramento River) and put the rest under water. The flood waters were exacerbated by the sediments washed down by the millions of tons by hydraulic mining, which filled the beds of the Sacramento, Feather and American rivers up to in Sacramento and also covered thousands of acres of Central Valley lands.[55][56] A flood in 1875 covered the city of Marysville and when it subsided the town's streets were filled with debris and rocks washed down from the "hydraulicking" going on upstream.[55][57]

Repeated floods and increased demand for Sacramento River water saw a plethora of massive changes to the environment beginning in the 20th century. An early project was undertaken to raise the entire city of Sacramento about above its original elevation.[58][59] This, however, was followed by engineering projects to try and stem the flows of water rather than defend against it. The engineering era of the 20th century on the Sacramento thus begun.[59]

Dams and water use

In the late 19th century through the 20th, California experienced an economic boom that led to the rapid expansion of both agricultural and urban infrastructure. The Central Valley was becoming a heavily developed irrigation farming region, and cities along the state's Pacific coast and the Sacramento and San Joaquin rivers were growing rapidly, requiring ways to manage the river's water to prevent flooding (and resulting economic loss) on one hand, and to ensure a consistent supply of it on the other. The U.S. Army Corps of Engineers and the state of California completed reports as early as the 1870s and 1880s that detailed the geography and water supplies of the Sacramento, Feather, Yuba and Bear rivers.[60]

Back in 1873, Colonel B.S. Alexander of the Army Corps of Engineers had written in his surveys of the Central Valley's hydrology and irrigation systems of a great network of pumps and canals that would take water from the water-rich Sacramento River basin into drought-prone South and Central California, especially the San Joaquin Valley. The Sacramento River is often said to receive "two-thirds to three-quarters of northern California's precipitation though it has only one-third to one-quarter of the land. The San Joaquin River watershed occupies two-thirds to three quarters of northern [central] California's land, but only collects one-third to one-quarter of the precipitation."[61]

During the Great Depression in the 1930s, the first plans for statewide water engineering projects emerged backed by first the Californian, then the United States government. The California State Water Project and Central Valley Project both began their rise to reality during this period. Both began as brainchilds of the state government, but because of lack of funds, the construction work and costs were shifted to the federal U.S. Army Corps of Engineers and U.S. Bureau of Reclamation. As the construction of dams, power plants and canals required immense labor, which was rare in the middle of the Depression, the government authorized Sacramento River dams and other structures as public works projects beginning in 1935.[60][62]

Construction work on Shasta Dam in June 1942
Construction work on Shasta Dam in June 1942
Construction of Shasta Dam, the main dam on the Sacramento, started in 1938 and was completed in 1945. Capable of absorbing enormous flood flows and storing the water for use in prolonged drought as well as navigation and electricity generation, it gave inhabitants of the Sacramento Valley nearly complete control over the whims of the river.[63][64] In the following decades, more dams huge dams hundreds of feet high and capable of storing millions of acre-feet of water were constructed on the Sacramento's main tributaries: the Pit, Feather and American. Folsom Dam, Oroville Dam and New Bullards Bar Dam, built in the 1950s and '60s for both the State Water Project and the Central Valley Project, are among the most important. With a firm water management system in place, the Sacramento River's flow was thus regulated and a highly controlled regime of irrigation and water diversions was able to begin.[61]

Part of the purpose of constructing dams on the Sacramento was to regulate flows for irrigation agriculture purposes. After the river's flow was under control, two major canals serving the western side of the Sacramento Valley the Tehama-Colusa and Corning Canals. Both starting at the Red Bluff Diversion Dam on the Sacramento, the two canals are and long respectively, and divert a total of over from the river to serve some of land.[65] A third major canal, the Sacramento River Deep Water Ship Channel, exists not for irrigation purposes but rather to facilitate navigation of large oceangoing ships from the Delta to the city of Sacramento. Built by the Army Corps of Engineers, the canal is long and is maintained to deep.[66]

In 1959, construction began on the final link for the Sacramento-San Joaquin River water system, the California Aqueduct.[60] A series of dams, dikes, channels and pump plants was constructed in the Delta to facilitate water flow from the Sacramento into this huge man-made river, which can carry up to of water.[67] From its origin at the Delta the canal runs some southwards through the west side of the San Joaquin Valley, providing irrigation water to farmlands along its length. The remainder is then powered over the Tehachapi Mountains via a pump lift. The Aqueduct's waters, which functionally extend the Sacramento River southwards, then run on to serve the enormous populace of California's south, supplying the needs of some 22 million people.[68][69]

Over the years, several other plans materialized to take water from other drainage basins into that of the Sacramento to bolster the river's petering discharge. A successful one was the Trinity River diversion, which sent over 90 percent of the flow of that river into the Sacramento through a tunnel under the Klamath Mountains.[70] Because of resulting ecological destruction and fish kills, less water is diverted today than a few decades ago. Others failed to take root one of the most notorious, the Klamath Diversion, proposed to send the entire flow of the Klamath River into the Sacramento Valley through a complex system of reservoirs, canals, flumes and tunnels.[71] Similarly, the Dos Rios Dam project would have diverted almost the entire flow of the Eel River to the Sacramento.[72] Both projects were defeated by locals' and environmentalists' opposition,[72] as well as, for the former, staggering costs.[71][73]


The Sacramento River and its drainage basin were originally abundant in multiple avian and aquatic species, but modern-day development has thinned populations of many species, especially riverine. The river's once-ample stretches of riparian zones and marshes, supported by its wide variations in flow, as well as the wetlands downstream in the Delta, have mostly been replaced by agricultural lands. The Sacramento supports 40 60 species of fish,[74][75] and 218 types of birds.[76] The basin is relatively abundant in endemic amphibian and fish species. It is surmised that between four and five million years ago, the Sacramento and Snake-Columbia River systems were somehow connected by a series of now-dry wetlands and river channels. Many of the fish in the present-day river are similar to those of the other, indicating a possible link sometime in the past. The Sacramento and San Joaquin also have the southermost runs of five species of anadromous fish.[75]

Red Bluff Diversion Dam, which sends Sacramento River water to a pair of irrigation canals near Red Bluff, is a major barrier to fish movement and migration in the river.
Red Bluff Diversion Dam, which sends Sacramento River water to a pair of irrigation canals near Red Bluff, is a major barrier to fish movement and migration in the river.
Wildlife along the Sacramento has been hurt severely by the heavy usage of Sacramento River water for agriculture and urban areas, and pollution caused by pesticides, nitrates, mine tailings, acid mine drainage and urban runoff.[19] Located along the Pacific Flyway, the sprawling marshlands of the Sacramento Valley were originally an important stop for migratory birds; only a few wetlands remain today, either preserved or artificially constructed.[77] Native bird populations have been declining steadily throughout the 19th, 20th and 21st centuries. Species that were once common but now are gone or endangered include the Southwestern Willow Flycatcher, Western Yellow-billed Cuckoo, Least Bell's Vireo, and Warbling Vireo. Another reason for dropping numbers are the introduction of non-native species, such as the "parasitic" cowbird, which steals the nests of other birds to use as its own.[78]

There were once 9 species of amphibians that used the Sacramento River,[79] but some have become extinct and the population of the others are declining drastically due to the loss of their habitat. Amphibians originally thrived in the marshes, sloughs, side-channels and oxbow cutoffs because of their warmer water, abundance of vegetation and nutrients, lower population of predators, and slower current. Encroachment of agricultural and urban land has eliminated most of this habitat. This population once included several species of frogs and salamanders; the foothill yellow-legged frog and western spadefoot are listed as endangered species.[80]

The riparian areas along the Sacramento once totaled more than ; today only about remains. Much of it consists of restored stretches, and there is also a significant amount of artificial wetland in the watershed. River control has prevented the Sacramento from its natural flooding, braiding and course-changing patterns, which are important for the maintenance of existing wetlands and the creation of new ones. Since the 1860s, the river has been mostly locked in its channel, which once could shift hundreds of feet or even several miles in a year because of floods. These wetlands originally flooded every winter and spring, but levee construction, agricultural encroachment and the construction of dams upstream have also eliminated the flooding process. Today about of the river s riparian forests are undergoing active restoration.[81][82]

Anadromous fish

Second only to the Columbia River on the west coast of the United States in Chinook salmon runs, the Sacramento and its tributaries once supported a huge population of this fish. Millions of salmon once swam upstream to spawn in the Sacramento; as recently as 2002 eight hundred thousand fish were observed to return to the river.[83][84]

Starting in the 20th century, dam construction blocked off hundreds of miles of salmon-spawning streams, such as the upper Feather and American Rivers, and the entirety of the Pit and upper Sacramento rivers. Pollution from farms and urban areas took a heavy toll on the river's environment, and heavy irrigation withdrawals sometimes resulted in massive fish kills. Since 1960, when the big pumps at the head of the California Aqueduct in the Delta began their operation, the outflow of fresh water into the Pacific has been reduced to a trickle leaving the fish confused as to where to go, resulting in many generations dying off because they have not been able to find their way upstream. In 2004, only 200,000 fish were reported to return to the Sacramento; in 2008, a disastrous low of 39,000.[85][83][86]

In 1999, five hydroelectric dams on Battle Creek, a major tributary of the Sacramento River, were removed to allow better passage of the fish. Three other dams along the creek were fitted with fish ladders. The river is considered one of the best salmon habitats in the watershed because of its relatively cold water and the availability of ideal habitat such as gravel bars.[87][88]

By the late 20th and early 21st centuries, the government blamed crashing fish populations on overfishing, especially off the Northern California and Oregon coast, which lie directly adjacent to the migration paths of Sacramento River salmon. This has resulted in a ban on coastal salmon fishing for several years since 2002.[89] The Red Bluff Diversion Dam, although not a large dam and equipped with fish passage facilities, also presents a major barrier. Because of inadequate design, roughly 25 40% of the incoming fish get blocked by the dam each year. The dam has also become a "favorite spot" for predatory fish to congregate, feasting on the salmon that get trapped both above and below the dam.[90] As of 2010, the salmon run has shown slight signs of improvement, probably because of that year's greater precipitation.[91]

In 1995, a gate on the Folsom Dam on the American River broke open, causing the river's flow to rise by some . The water traveled down the Sacramento and washed into the Pacific; the influx of fresh water was such that it confused thousands of anadromous fish to begin migrating up the river, thinking that the river had risen because of late-autumn storms.[92]


Delta the Whale in the Sacramento River
Delta the Whale in the Sacramento River
Marine animals such as whales and sea lions are occasionally found far inland after navigating the river for food or refuge and then losing track of how to get back to the Pacific Ocean. In October 1985 a humpback whale affectionately named "Humphrey the humpbacked whale" by television media traveled up the Sacramento River before being rescued. Rescuers downstream broadcast sounds of humpback whales feeding to draw the whale back to the ocean.[93]

On May 14, 2007, onlookers and media spotted two two humpback whales traveling the deep waters near Rio Vista. The duo, generally believed to be mother and calf (Delta, the mother and Dawn, her calf), continued to swim upstream to the deep water ship channel near West Sacramento, about inland. There was concern because the whales had been injured, perhaps by a boat's propeller or keel, leaving a gash in each whale's skin. The whales were carefully inspected by biologists and injected with antibiotics to help prevent infection. After days of efforts to lure (or frighten) the whales in the direction of the ocean, the whales eventually made their way south into San Francisco Bay, where they lingered for several days.[94] By May 30, 2007, the cow and calf apparently slipped out unnoticed under the Golden Gate Bridge into the Pacific Ocean, likely under cover of night.[95][96]


For a river of its size, the Sacramento is considered to have fairly clean water. However, pollutants still flow into the river from many of its tributaries and man-made drains or channels. Pesticide runoff, especially DDT, is one of the largest problems faced today, because of the valley's primarily agricultural economy. Increased erosion caused by the removal of riparian vegetation and the runoff of fertilizers into the river have led to occasional algae blooms, though the water is usually cold because of the regulation of dams upstream. Other pollutant sources include urban runoff, mercury and even rocket fuel that was reported to have leaked near the American River from an Aerojet extraction project.[97][98][99]

Mercury pollution created by mining and processing activities during the California Gold Rush still has a profound impact on the Sacramento River s environment. The toxic substance was widely used by miners to separate gold from the surrounding rocks and dirt, and was disposed of by allowing it to evaporate. Most of the mercury was mined in the Coast Ranges to the west of the Sacramento River; mines in these mountains produced roughly 140,000 tons of mercury to serve the Gold Rush. When the gold rush ended, most of the mines were closed but toxic acidic water and chemicals continue to leak from within, into west-side Sacramento tributaries such as Cache Creek and Putah Creek. In the east, mercury that permeated into the ground has contaminated several aquifers that feed rivers such as the Feather, Yuba and American. Even the evaporated mercury posed problems so much of it was used that significant concentrations still linger in the air in many places. Mercury pollution continues today and will probably continue for decades or centuries into the future.[4][100]

In July 1991, a train derailed near Dunsmuir, California alongside the Sacramento River. A tank car split open, spilling about 19,500 gallons of the pesticide metam sodium into the river. The chemical formed a stinking, bubbling, green glob that moved down the river, killing everything in its path. More than one million fish were killed, including at least 100,000 rainbow trout, and thousands of other aquatic creatures as well as nearby trees. Next, the green glob entered Shasta Lake, California s largest reservoir. Fortunately, a system of aerating pipes at the bottom of the lake had been set up to dissipate the chemical, reducing it to almost nothing by the 29th, preventing further environmental destruction. The tank car carrying the metam sodium through California was of a type that the National Transportation Safety Board said had a high incidence of failure in accidents. Furthermore, the tank car was not labeled, so the train s crew didn t know that they were hauling a dangerous chemical.[101][102]

See also


Works cited

External links

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