The water level in Lake Shasta, California’s largest reservoir, had plunged to less than a third of normal by the end of last year. Then came the El Niño rainfall, which by April had tripled the volume of water in the lake. The story is similar in Trinity Lake, part of the same network of federal projects in the far northern portion of the state that regulate the flow of water to the Sacramento River on its journey south toward the Sacramento-San Joaquin River Delta and San Francisco Bay.