Aquatic Herbicide and Algaecide Applications in the SWP in 2023


DWR’s Operations and Maintenance staff will be applying herbicides and algaecides to several facilities throughout the State Water Project (SWP) in 2023. Treatments will occur on an as-needed basis to control algae and aquatic weeds. The herbicides to be used may include copper, endothall, and/or diquat based compounds.

Locations throughout California to be treated include, but are not limited to, the South Bay Aqueduct, Dyer Reservoir, Patterson Reservoir, Clifton Court Forebay, O'Neill Forebay, the California Aqueduct, the Coastal Branch Aqueduct, Pyramid Lake, Castaic Lake, East Branch Aqueduct, Silverwood Lake, Perris Lake, Quail Lake, Thermalito facilities, and Los Banos Reservoir.

Public access to SWP water bodies will be restricted during aquatic herbicide treatments and notifications will be posted at the site. For questions, contact Tanya Veldhuizen at