Fresno Slough is a distibutary of the Kings River

Kings River (California)

The Kings River is a major river of south-central California. About long, it drains an area of the high western Sierra Nevada and the Central Valley. A large alluvial fan has formed where the river's gradient decreases in the Central Valley so the river divides into distributaries...

 that connects the North Fork Kings River (distributary) to the San Joaquin River

San Joaquin River

The San Joaquin River is the largest river of Central California in the United States. At over long, the river starts in the high Sierra Nevada, and flows through a rich agricultural region known as the San Joaquin Valley before reaching Suisun Bay, San Francisco Bay, and the Pacific Ocean...

. Until 1879, when irrigation diversions prevented it, Fresno Slough was also an outlet of the overflow waters of Tulare Lake

Tulare Lake

Tulare Lake, named Laguna de Tache by the Spanish, is a fresh-water dry lake with residual wetlands and marshes in southern San Joaquin Valley, California...

 into the San Joaquin River in flood years, when its level topped the 210 foot elevation.

Modern Diversions

Mendota Dam located at the confluence of the San Joaquin River and Fresno Slough delivers water to the south from Mendota Pool during the irrigation season, and delivers water to Mendota Pool and the San Joaquin River from the Kings River when the Kings River is flooding. Mendota Dam and Mendota Pool have been used for irrigation diversions since the late 1800s.