Sacramento River, the longest river in California. It begins in the mountains of northern California and flows southward some 380 miles (610 km) to Suisun Bay, an arm of San Francisco Bay. Principal tributaries are the Pit, Feather, and American rivers. Most of the river's course is through the Central Valley of California. South of Sacramento, the state capital, the Sacramento flows through an area barely above sea level. Shasta Dam, on the river north of Redding, is important for irrigation, flood control, and hydroelectric power. It impounds Shasta Lake, which is part of the Whiskeytown-Shasta-Trinity National Recreation Area.

In 1991 a pesticide spill near Dunsmuir, California, caused severe pollution in the upper Sacramento River.