This California river once carried thousands of salmon every year. A 1942 dam changed it forever, and scientists are still trying to bring them back

For much of its history, the San Joaquin River carried cold mountain water through California’s Central Valley, supporting forests, farms and some of the southernmost populations of Chinook salmon in the western United States. That connection began to disappear after the construction of Friant Dam in the 1940s, when large sections of the river were altered to supply irrigation water.