- Los Angeles River: This river flows through the heart of Los Angeles County, passing through several cities, including Los Angeles, Burbank, and Glendale. It is a major drainage system for the region and is approximately 51 miles long.
- San Gabriel River: The San Gabriel River is the largest river in Los Angeles County. It originates in the San Gabriel Mountains and flows through several cities, including Pasadena, Alhambra, and Long Beach, before emptying into the Pacific Ocean. The river is approximately 63 miles long.
- Santa Clara River: This river originates in the San Gabriel Mountains and flows through the Santa Clarita Valley before reaching Ventura County and eventually draining into the Pacific Ocean. The Santa Clara River is approximately 100 miles long.