Citing widespread contamination in state waterways, environmental groups planned to file a challenge to a loophole they say allows farmers to discharge toxic pesticides.
In a 33-page report titled "Water Woes," the California Public Interest Research Group and WaterKeepers Northern California said an analysis of state surface water shows 96 percent of sites tested over 10 years had some pesticide contamination.
"Almost every site where pesticides were sampled for, they were detected," said Jonathan Kaplan of WaterKeepers. "In half of those detected, the pesticides were found to be harmful. That says to me that we have a real problem, that says to me that the problem is widespread."
Many of places where the pesticides were detected are listed by the U.S. Environmental Protection Agency as impaired by pesticides. Salmon, bass, and smelt have been in decline in the waters for the past decade.
The groups plan to challenge a waiver granted 18 years ago by the Central Valley Regional Water Quality Control Board that exempts farmers from complying with the state's clean water act. They also plan to call for phasing out pesticides that continue to cause contamination.
Waivers from the state, which allow pesticide runoff to flow through irrigation ditches without regulation, are currently part of a three-year public review.
The state's largest farm group said farmers have made great strides in controlling pesticides in recent years and said it supports the review process.
"What they're doing now is by far more progressive or innovative than anything done before 1982," said Bob Krauter, a spokesman for the California Farm Bureau.
The regional water control board granted the conditional waivers to farmers after deciding that discharges would not be toxic to fish and other wildlife, said Rudy Schnagl, chief of the board's agricultural unit.
But the environmental report, which analyzes data compiled by the Department of Pesticide Regulation, concludes that contamination poses health threats to aquatic life and even humans who get some of their drinking water from the sampled waters.
In 10 years of testing creeks, rivers, drainage basins, and sloughs -- most in the farm-rich Central Valley -- the DPR analyzed 92,000 samples from 133 locations.
The study found pesticides:
* in 128 sites, or 96 percent.
* in 8,500 samples, or 9 percent.
* exceeded aquatic or human health criteria 51 percent of the time they were detected.
* frequently were among five pesticides considered hazardous and linked to cancer, nervous system damage, hormone disruption, or groundwater contamination.
The DPR's database is not comprehensive, however, and although it contains useful information, it's not conclusive, said spokeswoman Veda Federighi. The majority of pesticide detections were below levels of health or water quality concern.
The agency has begun monitoring surface water and is targeting how pesticides are getting into waterways to control the problem. Federighi said banning practices that lead to pollution, not banning pesticides, is the more prudent approach.
"Basically these reports call for widespread bans on pesticides," Federighi said. "That's a simple answer to a problem that's really complex. That's akin to saying 20 years ago that smog's a real problem so let's ban cars."
Kaplan said stronger action needs to be taken to protect fisheries and other aquatic life threatened by pesticides.
"We're effectively creating seasonal killing zones for aquatic life in the Central Valley," he said. "Major sport fisheries havebeen in decline over the last decade. We don't know how much is due to pesticides and how much is due to habitat loss. We know there are enough pesticides in high enough levels to kill off these fisheries."
If the petition signed by 68 environmental and public interest groups around the state succeeds, it would require permits to allow pesticide runoff.
"We have a water shortage problem already," said Teresa Olle, an author of the study. "We don't have the luxury of ruining our water sources."