 The drainage basin of the Merced River is located in the central Sierra Nevada , spreading across 1 @,@ 726 square miles ( 4 @,@ 470 km2 ) . It can be characterized as the slightly smaller southern companion of the Tuolumne River , the major Sierran river just north of the Merced . On the south , the basin borders on the headwaters of the San Joaquin River itself . The Merced River watershed includes the subwatersheds of Illilouette , Echo , Tenaya , Yosemite , Bridalveil , Cascade , and Dry Creeks , as well as the South and North forks of the river , of which the South Fork , at 43 miles ( 69 km ) long , is the largest . Tributaries to the South Fork include Bishop , Rail , Alder and Chilnualna Creeks . There are also many lakes in the watershed of the Merced River , including Merced Lake , Tenaya Lake , the Chain Lakes , May Lake , Lake McClure , and Lake McSwain . 
