The San Gabriel River is a mostly-urban waterway flowing 58 miles (93 km) southward through Los Angeles and Orange Counties, California, in the United States. It is the central of three major rivers draining the Greater Los Angeles area, the others being the Los Angeles River and Santa Ana River.
The river's watershed stretches from the rugged San Gabriel Mountains to the heavily developed San Gabriel Valley and a significant part of the Los Angeles coastal plain, emptying into the Pacific Ocean between the cities of Long Beach and Seal Beach. The San Gabriel once ran across a vast alluvial flood plain, its channels shifting with winter floods and forming extensive wetlands along its perennial course, a relatively scarce source of fresh water in this arid region.