The Merced River , in the central part of the U.S. state of California, is a 145-mile (233 km)-long tributary of the San Joaquin River flowing from the Sierra Nevada into the Central Valley. It is most well known for its swift and steep course through the southern part of Yosemite National Park, and the world-famous Yosemite Valley. The river's character changes dramatically once it reaches the foothills and the lowlands, becoming a slow-moving waterway meandering through irrigated fields.
Of the fish, there were 26 species found in the lower Central Valley portion of the river, including Sacramento sucker, smallmouth bass, largemouth bass and carp, all but three of which are resident species, and some of which were intentionally introduced by humans. The three anadromous fish species that still use the lower Merced are the chinook salmon, Pacific lamprey and striped bass. The upper section of the river, defined as the stretch from Lake McClure to the headwaters, had 11 species of fish.