The Los Angeles area is divided into three main watersheds.

The Los Angeles River, which drains runoff from the north side of the Santa Monica Mountains including the San Fernando Valley, Glendale, Downtown LA area, and most of the adjacent cities along the Long Beach Freeway corridor. This entire watershed discharges into the San Pedro Bay.

The Ballona Creek watershed covers the south side of the Santa Monica Mountain range including West LA, Santa Monica, Culver City, Inglewood, and every beach city facing the Santa Monica Bay (i.e. Manhattan Beach, Redondo Beach) up to Point Fermin.

The Dominquez Channel watershed covers most of the South Bay area.