During severe weather events or seasons of heavy rain, the two rivers that surround the City of Pico Rivera — the San Gabriel River and the Rio Hondo River — flow into the Whittier Narrows Reservoir to help prevent the two rivers from flooding into Pico Rivera neighborhoods and communities beyond.

The federal government has identified the Whittier Narrows Dam as the highest priority of the 13 highest risk dams in the United States. If the dam were to fail, it could flood up to 25 cities in the region, from Pico Rivera all the way to Long Beach. Impacts of such a catastrophic event may include significant loss of life, damage to property, and major economic and environmental consequences.