The Russian River (Southern Pomo: Ashokawna, ) (Russian: русская река) is a southward-flowing river that drains of Sonoma and Mendocino counties in Northern California. With an annual average discharge of approximately 1,600,000 acre feet (2.0 km3), it is the second-largest river (after the Sacramento River) flowing through the nine-county Greater San Francisco Bay Area, with a mainstem long.

Deriving its name from the establishment of colonial outposts by the Russian-American Company near its course, during the beginning of the 19th century, the river is today a significant body of water for recreation and agriculture and represents, as a result of its damming and the consequent creation of Lake Mendocino, a significant water source for several of the Northern California counties through which it runs.

Ecologically, the river is home to the Russian River tule perch, a distinctively endemic species of freshwater surfperch, as well as significant populations of steelhead trout, Coho and Chinook salmon. During its initial exploration, large numbers of otters and beavers were also identified, and subsequently hunted. Presently, toxic cyanobacteria of the genus Microcoleus have also represented a significant element of the Russian River ecosystem, including a species from that genus found only in the river as of yet.

Names

The Southern Pomo know the river as Ashokawna (), "east water place" or "water to the east", and as Bidapte, "big river." Juan Rodríguez Cabrillo and his expedition may have travelled as far north as the Russian River in November 1542 before storms forced them to turn back south towards Monterey. The earliest Slavic name for the river, Slavyanka, appears on a Russian-American Company chart dated 1817. In 1827 the Spanish called it the San Ygnacio, and in 1843 the Spanish land grant referred to it as Rio Grande.

The river takes its current name from Russian Ivan Kuskov of the Russian-American Company, who explored the river in the early 19th-century and established the Fort Ross colony northwest of its mouth. The Russians called it the Slavyanka River, meaning "Slav River". (Slavyanka in Russian means "Slavic woman".) They established three ranches near Fort Ross, one of which, the Kostromitinov Ranch, stretched along the Russian River near the mouth of Willow Creek. The redwoods that lined its banks drew loggers to the river in the late 19th century.

According to the USGS, variant names of the Russian River include Misallaako, Rio Ruso, Shabaikai, and Slavyanka.

Course

The Russian River springs from the Laughlin Range about east of Willits in Mendocino County. It flows generally southward to Redwood Valley, then past Calpella, where it is bordered by U.S. Route 101, to join the East Fork Russian River just below Lake Mendocino.

From there the Russian River flows south, past Ukiah through the Ukiah Valley and Hopland through the Sanel Valley, and crosses into Sonoma County just north of Cloverdale. Closely paralleled by U.S. Route 101, it descends into the Alexander Valley, where it is joined by Big Sulphur Creek. It flows south past Cloverdale, Asti, and Geyserville.

From there, the Russian River flows west, east of Healdsburg, Maacama Creek joins the Russian River. After it makes a series of sweeping bends, the Healdsburg Memorial Bridge carries Old Redwood Highway over the river just upstream of U.S. Route 101's Healdsburg crossing. It receives water from Lake Sonoma via Dry Creek. The river turns westward, where it is spanned by the Wohler Bridge, and it is joined by Mark West Creek north of Forestville, followed by Green Valley Creek to the south. The river passes Rio Nido and Guerneville. In that area, State Route 116 parallels the river, bordering it past Guernewood Park and Monte Rio.

Austin Creek enters from the north before the River passes through Duncans Mills. State Route 1 crosses over the river before it flows into the Pacific Ocean between Jenner and Goat Rock Beach. The Russian River estuary is recognized for protection by the California Bays and Estuaries Policy.State Water Resources Control Board Water Quality Control Policy for the Enclosed Bays and Estuaries of California (1974) State of California The mouth is about north of the San Francisco Bay's Golden Gate bridge.

The lower Russian River is a popular spring, summer, and fall destination for navigation and recreation. It is very safe at that time for swimming and boating, with a gentle current.State of California Water Quality Control Plan North Coastal Basin 1B July 1975 p.13 The river is dangerous in the winter, with swift current and muddy water.

Geology The geographer R. S. Holway described the Russian River in his 1917 paper "The Russian River: A Characteristic Stream of the California Coast Ranges". Originally, the Russian River was one of several rivers draining westward from the Mayacamas Mountains through the Mendocino Plateau to the sea, a region lifted up by tectonic forces. The Navarro River drained from the Cobb Mountain area, while the Russian River drained from the Mt. St. Helena area. Being at a lower elevation, the Russian River began cutting north into the drainage area of the Navarro River. Eroding up a fault line in Alexander Valley, the Russian River intersected the Navarro River just north of Cloverdale. This resulted in the stream capture of Big Sulphur Creek (formerly the upper Navarro River) and the north fork of the Navarro River, going north to Hopland and to Ukiah. The high valleys were eroded into rocky canyons for ten miles north of Cloverdale and for five miles east of Cloverdale.

After establishing a connection to Clear Lake, the Russian River was beheaded from Clear Lake by a slide at Cow Mountain, east of Ukiah. Now Clear Lake flows into the Sacramento River.Holway, page 13 The river incised a canyon into Fitch Mountain at an early time, before land levels were eroded to their present levels.Holway, pages 20–21 The river was prevented from flowing south into San Pablo Bay by a 113-foot high ridge at Cotati.Holway, pages 25–26 Guerneville is built on an abandoned meander of the river. Near Guerneville, another meander cut short Smith Creek.Holway, page 29

A 1977 survey published in the journal Micropaleontology identified 29 species of foraminifera in the estuary of the river, collected from three ecologically different regions. Characterizing the estuary with respect to degrees of mixture or separation demonstrated between saltwater and freshwater, the survey found the highest diversity of species was recorded from offshore stations, as well as those occurring towards the mouth of the river.

The Mendocino Plateau is a part of the Franciscan Complex.

River modifications A portion of the Eel River is diverted to headwaters of the Russian River in Potter Valley, via a scheme known as the Potter Valley Project. The Sonoma County Water Agency draws drinking water from the Russian River for sale to several hundred thousand residents of Sonoma, Mendocino, and northern Marin counties. Santa Rosa's Laguna Wastewater Treatment Plant treats sewage from several communities to tertiary standards and returns some of it to the river by way of the Laguna de Santa Rosa.

Water transferred from the Eel River and released from Lake Mendocino flows through the Russian River channel to withdrawal points in Sonoma County. Although this method of transport supports aquatic and riparian zone habitats, it is vulnerable to chemical contamination from transportation accidents. These are an issue at points where the river is in close proximity to highway 101 and Northwestern Pacific Railroad transportation corridors, in locations like the canyon between Cloverdale and Hopland. This vulnerability was demonstrated in March 1982, when a tank car of formaldehyde was vandalized in Ukiah. Emergency response personnel were able to clean up approximately half of the spilled, and a fortuitous combination of Lake Mendocino reservoir inventory and late winter storms helped flush the remainder through the river and into the ocean before local water storage inventories were exhausted.

The Russian River reached flood stage of at Guerneville about five times per decade through the last half of the 20th century. Historic flood peaks were in February 1986, in January 1995, in December 1955, in December 1964, and in February 1940. Through effective use of Lake Mendocino and Lake Sonoma flood capacity, the river has exceeded flood stage at Guerneville less frequently in the 21st century. In late February 2019, however, it flooded to levels comparable to 1986.

Ecology

Fish populations The river provides wildlife habitat including warm and cold freshwater habitat for fish migration and spawning. It is of historical note as one of two Northern California coastal rivers mentioned in the early nineteenth century by Russian explorer K. T. Khlebnikov as hosting sturgeon along with the Pajaro River. These were presumably white sturgeon (Acipenser transmontanus), the largest freshwater fish in the United States. Khlebnikov stated in his "1820 Travel Notes": "Mr. Kuskov had sent two baidarkas to the Slavyanka River to catch sturgeon, and they returned today with ten fish... the largest one exceeding two arshins (4.67 feet) long". Moyle's Inland Fishes of California states that there were historic runs of white, but not green, sturgeon in the Russian River.

The Russian River is the largest river in the Central California Coast steelhead trout (Oncorhynchus mykiss) distinct population segment. Natural waterfalls and the two major dams, Warm Springs (built in 1982) and Coyote (built in 1959), have isolated anadromous steelhead from its non-oceangoing rainbow trout form above the impassable barriers. Recent genetic studies on steelhead collected at 20 different sites both above and below passage barriers in the watershed found that despite the fact that 30 million hatchery trout were stocked in the river from 1911 to 1925, the steelhead remain of native and not hatchery stock.

Until recently, most reviews indicated that Chinook salmon (Oncorhynchus tshawytscha) were always scarce on the Russian River. However, in 2007, the Sonoma County Water Agency completed a comprehensive re-evaluation of historical records, coupled with a five-year monitoring program using underwater cameras at two fish ladders just north of Forestville. They found that Chinook salmon always were, and still are, "a relatively abundant, widely distributed, and naturally self-sustaining population". The authors found historic information dating to 1881 suggesting the presence of an ancestral population, and their genetic analysis found the Chinook both above and below barriers to fish passage to be of native, and not hatchery stock.

In 2001 the Coho salmon (Oncorhynchus kisutch) had dwindled to less than four returning spawners per year. These low numbers were the catalyst for the Russian River Coho Salmon Captive Broodstock Program, a recovery effort in which offspring from hatchery-reared adults are released into the river system. In 2011, biologists estimate that more than 190 adult coho may have returned to the Russian River watershed, beginning with early storms in October and peaking in December. High priority tributaries for restoration of stream flows and habitat for Coho include Dutch Bill, Grape, Green Valley, Mark West and Mill Creeks.