The beating heart of California’s massive system of capturing, storing and distributing water is the Sacramento-San Joaquin Delta. Water flows into the West’s largest estuary from the Sacramento, San Joaquin and several lesser rivers that drain the state’s mountain chains on its northern and eastern edges. While most of the water continues into the Pacific Ocean, giant pumps on the southern edge of the Delta suck much of it into canals supplying San Joaquin Valley farms and Southern California cities as far south as San Diego.