Nine of every 10 illegal marijuana farms raided in California this year contained traces of powerful and potentially lethal pesticides that are poisoning wildlife and could endanger water supplies, researchers and federal authorities said Tuesday.

That’s a jump from chemicals found at about 75 percent of illegal growing operations discovered on public land last year, and it’s six times as high as in 2012.

Federal and state officials launched a summer-long crackdown driven in part by new concern over the increase in the use of the highly toxic pesticide carbofuran.

Researcher Mourad Gabriel, one of the few researchers studying the ecological impact of illicit grow sites, said the pesticide is so powerful that a quarter-teaspoon can kill a 300-pound (136-kilogram) bear.

He and fellow researchers at the Integral Ecology Research Center in northwestern California found 89 percent of sites this year have been confirmed or are strongly suspected to be contaminated with what he called “highly deadly toxic chemicals.”