Many dangerous pesticides are found in California's water and sediments--frequently at levels above concentrations lethal to zooplankton, small aquatic organisms eaten by fish. Insecticides diazinon and chlorpyrifos and herbicides simazine, diuron, and EPTC are the pesticides most commonly detected because of their frequent use and high water solubility.
California urban and agricultural stormwater and irrigation run-off carry pesticides into surface waters, which results in toxic pulses of pesticides--a direct violation of the Clean Water Act and the Basic Plans set by the Regional Water Quality Control Boards. These toxic pulses create lethal conditions for the small aquatic organisms that fish eat. The pesticides most commonly found at toxic levels during these pulses are diazinon and chlorpyrifos from sprays to dormant almond and stone fruit orchards.
Conventional agriculture is the leading but least regulated source of water pollution
In 1982, the Central Valley Regional Board "conditionally waived" agricultural discharges from the California's clean water laws' reporting and permitting requirements. For decades, farmers have been allowed to discharge wastes into the state's waters without requirements to monitor or implement measures to control pollution.
Since 1982, both state regulators and the U.S. Environmental Protection Agency (EPA) have determined that agricultural pollution causes or contributes to the pollution of virtually every significant waterway in the Central Valley.
According to the U.S. EPA's 2002 list of impaired waterbodies, over 635 miles of rivers and streams in the Central Valley, including the Sacramento and San Joaquin Rivers and Delta, are so polluted by agricultural pesticides that they are unsafe for uses such as fishing, swimming, and drinking.
Farm runoff that reaches the Sacramento and San Joaquin Rivers contaminates drinking water supplies for millions of Californians in the Central Valley, the San Francisco Bay Area and Southern California.
Pesticides, pathogens, nitrates and salts have been detected in drinking water sources for at least 46 California counties. The Department of Pesticide Regulation detected pesticides in 96% of Central Valley locations tested, and over half of these detections exceeded unsafe levels for aquatic life and drinking water consumption.