The Los Angeles and San Gabriel Rivers originate high in the mountains of the Angeles National Forest before flowing down into the San Fernando and San Gabriel Valleys. These valleys contain important groundwater basins that have been relied upon for freshwater. From the valleys, the rivers continue their journey across the coastal plain of Los Angeles, eventually reaching the Pacific Ocean via the Los Angeles-Long Beach Harbor.
Over time, urbanization has greatly impacted these rivers. Dams and concrete channels now restrict the natural flows, resulting in lost habitat and reduced public access. Water diversions for groundwater recharge and wastewater discharges have also dramatically altered the rivers’ hydrology. Despite these changes, the upper watersheds remain largely pristine and host a diverse array of wildlife species, many of which are now endangered or threatened. Protecting these sensitive ecological areas while meeting the water needs of a major metropolitan region remains an ongoing challenge.