Baldwin Lake is a sag pond in the Los Angeles County Arboretum and Botanic Garden, which is in the San Gabriel Valley of Southern California, south of the San Gabriel Mountains. The pond, arboretum, and botanic garden are all within the city of Arcadia. The pond is fed by stormwater and natural springs; water flows out of the pond to the aquifer at Raymond Fault, and on to the Rio Hondo. Baldwin Lake is part of the Los Angeles River watershed.