The Clean Water Act requires states to monitor waterways and submit a list of problems to the U.S. Environmental Protection Agency (EPA).
Last year, California updated its findings from 2006.
EPA Water Director Alexis Strauss said over that time the number of rivers, streams and lakes in California registering toxicity rose 170 percent.
"I think that this increased observation really has to do more with the focused monitoring and assessment of previously existing toxicity,” said Strauss. “I don't think we have any huge spike in new toxicity."
The EPA found the most common contaminants to be pesticides, bacteria and metals. Strauss said this information lays the groundwork for more efforts to get at the sources of toxicity.
It will be used to develop local and federal pollution control plans.
