The Stanislaus River (Spanish: R�o Estanislao) in the U.S. state of California is one of the largest tributaries of the San Joaquin River. The river is 95.9 miles (154.3 km) long and has north, middle and south forks. It drains a long, narrow area of the western Sierra Nevada and the northern part of the San Joaquin Valley.
The north and south forks meet several miles upstream from New Melones Lake and the middle fork joins the north fork a few miles before that.
The Stanislaus River is extensively dammed and diverted. Donnells Dam on the middle fork forms Donell Lake, high in the Sierra Nevada. Downstream is Beardsley Dam, which forms Beardsley Lake. McKays' Point Diversion Dam diverts water on the north fork for hydroelectricity production and domestic use. New Spicer Meadow Reservoir is located on Highland Creek, a tributary of the North Fork. The South Fork is dammed at Lyons Dam and Strawberry Dam, both owned by Pacific Gas and Electric.
The New Melones Dam blocks the river after the confluence of all three forks. Downstream from New Melones Lake, there is Tulloch Dam, which forms Tulloch Reservoir, and Goodwin Dam, which is the first major barrier for anadromous fish on the Stanislaus River. In fact, the Stanislaus River historically supported a large population of spring-run chinook salmon which was extirpated with the construction of Goodwin Dam. Below Goodwin Dam, the Stanislaus eventually meets the San Joaquin River and flows into the Sacramento-San Joaquin River Delta.
The Stanislaus is famous for a political battle over building the dam (which now forms New Melones Lake). The non-profit organization Friends of the River was formed to manage the fight, and has since worked to save rivers throughout California. Prior to the construction of the dam and the flooding of the river, the lower Stanislaus was one of the most rafted whitewater runs in the United States. Rafting is still popular on the north fork of the Stanislaus and on the Goodwin Canyon section of the main Stanislaus. In long periods of drought, the Camp Nine run comes back as the lake level drops. In the early 1990s, this section was runnable for 3 years, with the river reaching the Highway 49 bridge before the rains brought the lake level all the way up above the put-in.
The river is named for Estanislao, a Miwok leader from Mission San Jos�, who led a band of 400 former mission acolytes against the Mexican government in 1828 and 1829. The band made its base along the banks of the river, then known as the R�o de los Laquisimes. The word Laquisimes could be a Spanish loanword referring to the "Lakisamni", an Amerindian tribe that lived on the Stanislaus near Knights Ferry.