Diazinon Reduction in the Feather and Sacramento Rivers

Water quality in nine watersheds within the Lower Sacramento Basin in California’s Central Valley has been improved using the watershed approach to control pesticide pollution. In the early 1990’s state and federal natural resource agencies identified elevated levels of the pesticide Diazinon in the Sacramento and Feather Rivers and linked Diazinon to observed aquatic toxicity. The California Central Valley Regional Water Quality Control Board (CVRWQCB) added four river segments to California’s 1994 Clean Water Act (CWA) Section 303(d) List of Impaired Waters (303(d) List) due to aquatic toxicity caused by diazinon. By 2002, CVRWQCB had identified Diazinon impairments in eleven Sacramento and Feather River waterways covering 196 river miles.

Community, business, education, research, and regulatory activities resulted in the reduction of Diazinon concentrations in the Sacramento and Feather River systems. A diverse group of stakeholders, motivated by the basic need for clean water and impending regulation, developed a variety of tools to reduce the use of Diazinon and control polluted runoff from reaching waterways. Their combined efforts resulted in the removal of 79 river miles from the 303(d) List for diazinon impairments by 2010.

The success of the watershed approach in reducing diazinon impairments in Central Valley water bodies is a model for future water quality restoration efforts. Continuing watershed-based pollution control activities can successfully address ongoing water quality challenges in the Lower Sacramento Basin by combining community-based watershed activities with regulation. Persistent water quality problems in the Central Valley include the remaining 117 Diazinon– impaired river miles, the replacement of diazinon with pyrethroid pesticides (highly toxic in the aquatic environment), and thousands of river miles that have other pesticide, nutrient, metals and toxicity water quality impairments in the Central Valley. Lessons learned from these efforts focus future actions and strengthen partnerships that continue to work toward improving water quality in the Central Valley and beyond.