San Joaquin (săn wäkēn´), river, c.320 mi (510 km) long, rising in the Sierra Nevada, E Calif., and flowing W then N through the S Central Valley to form a large delta with the Sacramento River near Suisun Bay, an arm of San Francisco Bay. The San Joaquin is navigable c.40 mi (60 km) for oceangoing vessels to Stockton. The Mokelumne, Tuolumne, Merced, and Fresno are its chief tributaries. The wide southern part of the Central Valley basin between the Sierra Nevada and the Coast Range is usually called the San Joaquin Valley, although the southern half of this area is drained by independent rivers such as the Kings and the Kern. Between Stockton in the north and Bakersfield in the south are many cities, notably Fresno, Modesto, and Merced.
The Central Valley project, undertaken largely to bring surplus water from the north to make the San Joaquin Valley more fertile, has as one of its units Friant Dam on the San Joaquin; the San Luis Dam is on the San Luis River, and the Delta-Mendota Canal parallels the lower San Joaquin on the west. The diversion of much of the river's water to irrigation, however, caused large stretches of the river from below the Friant Dam to the Merced River to run dry. An agreement in 2006 between the Bureau of Reclamation, the Natural Resources Defense Council, and the Friant Water Users Authority called for restoration of 153 mi (246 km) of the river through the release of water from the Millerton Reservoir behind the Friant Dam.