The headwaters of the Mokelumne River originates in the Sierra Nevada mountain range as three branches that flow into Pardee Reservoir. Below that, the Mokelumne River enters the Camanche Reservoir in the foothills of the Sierras. The lower river crosses California's Central Valley flowing through Lodi and
eventually into the San Joaquin River.
The name "Mokelumne" is a Native American term from the Miwok tribe, meaning people of the fishnet.
Most years, the main stem above Pardee Reservoir runoff period extends into July. Most of the fishing opportunities fall between July and October. Wild brook trout are present in most of the uppermost headwater areas. Rainbows are stocked but there are also plenty of wild brown trout. They migrate out of the lake into the upper river to spawn during early Autumn.
The river has a good variety of aquatic insects, some crustaceans and plenty of baitfish for the trout to eat. Terrestrial insects also play a role in the summer. Most mayflies are Blue-winged Olives, Pale Morning duns, Tricos and many others depending on the section of the river. Caddisflies are also plentiful and consist mostly of Little Blacks, Spotted Sedges and Green Sedges. October Caddis are present in some sections. There are several stonefly species as well. Little Yellows are the most plentiful.
The tailwaters below the reservoirs (Lake Commanche) has a Steelhead run as well as resident trout. Although steelhead catches have been low during past years, they have improved greatly in recent years. Chinook Salmon are also returning to the river. The lower river is best fished from a drift boat. One reason is that it flows mostly through private property.