In a typical year, about half of our water comes from the Sierra Nevada range. If flows off the mountains then through the Sacramento-San Joaquin Delta before reaching Castaic Lake via the State Water Project aqueduct.

This imported water is then withdrawn from Castaic Lake and flows through large underground pipelines to supply SCV Water's treatment plants, the Earl Schmidt Filtration Plant and the Rio Vista Water Treatment Plant. 

Click here for more information on SCV Water's imported water supply.

Quagga mussels can pose problems at lakes across California, including Castaic Lake. The invasive species are extremely destructive, clogging pipes used for drinking water, irrigation and hydropower, and necessitating extensive containment efforts. They also block boat motors and harm native fish by altering the habitat and the food web. After quagga mussels were discovered in Castaic Lake in 2021, the California Department of Water Resources (DWR) implemented additional boating requirements at Castaic Lake, including requiring boats to be inspected and drained upon leaving Castaic Lake and Lagoon.