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. Decades later, a major restoration effort is attempting to repair that break. The San Joaquin River Restoration Program is reshaping parts of the river while working to return a lost salmon population and balance the needs of communities that depend on its water.How the 1942 construction of Friant Dam transformed the San Joaquin River The San Joaquin River once played an important role in the life cycle of Chinook salmon. Before large-scale water development transformed the landscape, salmon travelled upstream through the river system, including areas near the foothills of the Sierra Nevada. Spring-run Chinook were particularly dependent on the river’s cooler waters, spending months waiting in suitable habitats before beginning their journey back downstream.According to NOAA, that pattern changed after...