The American River watershed supports Mediterranean, temperate, and montane ecosystems, and it is the home of a diverse array of fish and wildlife.

In 1839, Swiss immigrant John Sutter established the New Helvetia settlement on the American River, near the present-day location of central Sacramento.

This large and extensive mining practice washed away entire mountainsides and heavily polluted all the waterways, including the American River, creating an environmental disaster for inhabitants, fish, birds, and other flora and fauna.

Newly elected Governor Leland Stanford had to travel to his inauguration by rowboat; shortly after, the state government moved temporarily to San Francisco.

A significant contributor to the flood damage was the debris washed down by hydraulic mining, which had choked the river channel and reduced its capacity to drain floodwaters.

This status provides state and national recognition to protect the river's outstanding scenic, fish and wildlife, historic, cultural, and recreational values.

All three forks are known for their verdant canyons, forested ridges, massive rock formations, trails, back-country winter adventuring among snowy peaks, fishing and white water rafting.

In warmer winters much of the precipitation may fall as rain instead, causing flooding, but resulting in lower summer flows due to the lack of snow.

Due to California's highly variable weather patterns, runoff volumes in the American River can rise and fall drastically from one year to the next.

The American River Parkway incorporates historic Leidesdorff Ranch, a 35,000-acre (140 km2) cattle and wheat agribusiness owned by the "African Founding Father of California."

Jedediah Smith Memorial Trail, a meandering 32-mile (51 km) cycle path, hugs the river bank from Old Sacramento to Folsom Lake.

This dam creates the small Lake Clementine just north of the Foresthill Bridge and upstream of the confluence with the Middle Fork American River at Auburn.

The Middle Fork is used extensively for both motorized and non-motorized recreation, including fishing, white water rafting, bicycling (mountain and road), horseback riding, trail running and hiking.

Sacramento County in particular, where the main stem American River is located, is known for its cool winters and hot summers, with low average precipitation.

[21] The North, Middle and South Forks originate in alpine zones along the Sierra Crest and flow through subalpine, montane and temperate coniferous forests.

Native plants along the American River Parkway are adapted to a Mediterranean climate, are drought tolerant, and help support a balanced, healthy ecosystem.

The numerous hydroelectric dams upstream on the Middle and South Forks are not constrained by flood control requirements; rather, the needs of electricity and water supply govern their operation.

Folsom Dam was built in 1955 as a principal part of the Central Valley Project by the Army Corps of Engineers, and is operated by the Bureau of Reclamation.

The concrete and earth embankment structure is more than 5 miles (8.0 km) long and creates Folsom Lake, impounding 1.1 million acre-feet (1.4 km3) of water when full.

[29] The dam is a multipurpose facility that acts as a reservoir for flood control, irrigation, domestic and industrial use, as well as hydroelectric power generation, recreation, and fish and wildlife habitat.

[31] Eight hydroelectric plants on the South Fork are operated by Sacramento Municipal Utility District (SMUD) as the Upper American River Project.

The Upper American River Project produces 1.8 billion kilowatt hours in an average year, enough for about 20 percent of Sacramento's electricity needs.

[33] Chinook salmon are a threatened anadromous fish species that have historically used the American River as a location for an important part of their life cycle while in freshwater.

The project also included the introduction of small islands, loose woody debris, and larger boulders to advance the rearing habitat for the anadromous fish and increase biodiversity of the American River.

The land they protect helps the American River water quality by conserving and restoring wet meadows, wetlands, and riparian areas.

[38] The Water Forum actively works to enhance habitat for salmon and steelhead in the Lower American River in partnership with federal, state and local agencies.

The areas with rapids still feature scenic views and wildlife, which is what makes it the most popular whitewater rafting location in California [40] The California Office of Environmental Health Hazard Assessment has issued safe eating advice based on levels of mercury and polychlorinated biphenyl for fish caught from the section of the river that flows through Sacramento County.