Sacramento River: California's Largest River

The Sacramento River is the longest and largest river in California, flowing 445 miles from its source on the slopes of Mount Shasta in the Cascade Range south through the Sacramento Valley to the Sacramento-San Joaquin Delta, where it empties into San Francisco Bay. It drains 27,000 square miles — roughly a quarter of the state.

Introduction

The Sacramento is the linchpin of California's water system. Through the Central Valley Project and State Water Project, Sacramento River water is pumped hundreds of miles south to irrigate the San Joaquin Valley and supply the metropolitan areas of Southern California. No other river in the United States is more central to the water politics of an entire state.

Geography & Dimensions

• Length: 445 miles (716 km)
• Drainage Basin: 27,000 sq miles
• Average Discharge: 23,490 cu ft/s
• Source: Mount Shasta, Cascade Range

The Sacramento River rises near Mount Shasta at over 6,000 feet elevation, fed by springs, snowmelt, and rainfall from the southern Cascades and the northern Sierra Nevada. It flows south through a broad alluvial valley — the Sacramento Valley — flanked by the Coast Ranges to the west and the Sierra Nevada to the east. Major tributaries include the Pit, Feather, and American Rivers.

Shasta Dam, completed in 1945, impounds the Sacramento's largest reservoir at 4.5 million acre-feet. Below the dam, the river meanders through the Sacramento Valley, one of the most productive agricultural regions in the world. The river passes through the city of Sacramento, California's capital, before entering the vast Sacramento-San Joaquin Delta.

Water Infrastructure

• Shasta Dam: 602 feet tall, 4.5 million acre-feet storage
• Central Valley Project: Federal; delivers water to farms and cities
• State Water Project: State; pumps water to Southern California
• Oroville Dam: 770 feet — tallest dam in the United States

The Sacramento River is the most heavily engineered river in California. Shasta Dam on the upper Sacramento and Oroville Dam on the Feather River (the Sacramento's largest tributary) are the cornerstones of the federal Central Valley Project and California State Water Project, respectively. Together, these systems deliver water to over 25 million people and millions of acres of irrigated farmland.

Oroville Dam, at 770 feet, is the tallest dam in the United States. In 2017, its main spillway failed during heavy rains, forcing the emergency evacuation of 188,000 people — the largest dam-related evacuation in American history. The incident exposed the aging and sometimes dangerous state of California's water infrastructure.

Sacramento-San Joaquin Delta

• Area: 1,100 sq miles of waterways and islands
• Water Exports: Pumps export water to San Joaquin Valley and SoCal
• Levees: Over 1,100 miles of aging levees
• Earthquake Risk: Major earthquake could cause catastrophic levee failure

The Sacramento-San Joaquin Delta is a 1,100-square-mile maze of waterways, islands, and reclaimed farmland where the Sacramento and San Joaquin Rivers merge before flowing into San Francisco Bay. It is the hub of California's water system — massive pumps at the southern end of the Delta export water to the San Joaquin Valley and Southern California.

The Delta's islands are protected by over 1,100 miles of aging earthen levees, many built by hand in the 19th century. Most islands sit below sea level — some as much as 25 feet below — making them vulnerable to flooding. A major earthquake on nearby faults could trigger simultaneous levee failures, flooding multiple islands and allowing salt water to contaminate the freshwater supply for millions of Californians.

Salmon & Ecology

• Chinook Salmon: Four distinct runs (winter, spring, fall, late-fall)
• Winter-Run Chinook: Endangered — spawn below Shasta Dam
• Delta Smelt: Critically endangered indicator species
• Riparian Habitat: Over 90% lost to agriculture and development

The Sacramento River supports four distinct runs of chinook salmon — winter, spring, fall, and late-fall — each adapted to different spawning times and locations. The winter-run chinook, which historically spawned in cold streams above Shasta Dam, is now endangered. With its historic habitat blocked by the dam, the population depends entirely on cold water released from Shasta Reservoir into the river below.

The delta smelt, a small fish found only in the Sacramento-San Joaquin Delta, has become one of the most controversial species in American environmental politics. Listed as endangered, the smelt's decline is linked to water exports, habitat loss, and invasive species. Court-ordered protections for the smelt have sometimes restricted water exports, pitting environmentalists against agricultural and urban water users.

Challenges & Future

• Climate Change: Reduced snowpack shifting to more rain, earlier runoff
• Subsidence: Delta islands sinking due to peat soil oxidation
• Sites Reservoir: Proposed new reservoir to capture floodwater

Climate change is fundamentally altering the Sacramento River's hydrology. As temperatures rise, more precipitation falls as rain rather than snow, and snowpack melts earlier. This shifts the peak runoff from late spring to winter, when reservoirs may already be full, reducing the amount of water available for storage. By mid-century, the Sierra snowpack may decline by 50 percent or more.

The Sacramento River's future is the subject of intense political and legal battles. Proposals to build new reservoirs, construct a tunnel to move water through the Delta, and restore floodplains are all on the table. With 40 million Californians depending on a water system designed in the mid-20th century for a different climate, adapting the Sacramento River's management to the 21st century is one of the most important infrastructure challenges in the nation.

Key Facts

• The Sacramento River is California's longest at 445 miles, draining 27,000 square miles.
• It delivers water to over 25 million people through the Central Valley and State Water Projects.
• Oroville Dam, at 770 feet, is the tallest dam in the United States.
• Four distinct chinook salmon runs use the river, including the endangered winter-run.
• The Sacramento-San Joaquin Delta is protected by 1,100 miles of aging levees.

Fun Facts

• The Sacramento River is one of only a handful of rivers in the world that supports four separate runs of the same salmon species in one river system.
• In 2017, the Oroville Dam spillway crisis forced the evacuation of 188,000 people — the largest dam-related evacuation in US history.
• The Delta's islands are so far below sea level that if the levees fail, some islands would be under 25 feet of water.
• Mount Shasta, where the river originates, is a 14,179-foot volcano that last erupted around 1250 CE.

Final Thoughts

The Sacramento River is the foundation of California's water supply and agricultural economy, but its system is under unprecedented stress from climate change, aging infrastructure, and competing demands. How California manages this river in the coming decades will shape the future of the most populous state in the nation.