The Los Angeles River (also called: El Rio De Nuestra Senora La Reina De Los Angeles De Porciuncula or Porciuncula River; Spanish: River of the Angels; informally LA River) is a river flowing through Los Angeles County, California, in the United States. About 51 miles (82 km) long, it flows from Canoga Park south and west to its end at the Long Beach Harbor, in San Pedro Bay, part of the Pacific Ocean. The basin is rimmed by the San Gabriel Mountains, Santa Monica Mountains and Santa Susana Mountains, as well as several smaller mountain ranges. Much of the water that flows in the Los Angeles River flows in from tributaries that come from the mountains.
The river was once free-flowing, winding across a floodplain that occupied much of the Los Angeles Basin. With its frequent floods, it often changed course, causing erosion and depositing silt in other places. When the city of Los Angeles had its first settlers around the 1850s, the river was its main water source. With the opening of the Los Angeles Aqueduct in 1913, the Los Angeles River was no longer needed as a water source. Today, the Los Angeles River runs in a fixed course through a concrete channel for nearly its whole length. It is heavily polluted. The primary source of water during summer and fall is the Donald C. Tillman Water Reclamation Plant in Van Nuys. Plans for restoration of the river are being discussed.