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Water quality officials investigating pesticide found in Merced River

Scrambling to spray orchards during January’s rainstorms, a local orchard owner apparently sprayed trees illegally, fouling the Merced River.

The East San Joaquin Water Quality Coalition, a nonprofit serving as a buffer between local growers and the Central Valley Regional Water Quality Control Board, found a harmful pesticide in the river after multiple testing.

The group sampled the water at its Santa Fe Ave. site, near Ballico, on Jan. 24 and again this week. The pesticide found is an organophosphate, but it will be about a week before the exact pesticide is known, said Perry Klassen, executive director of the coalition.

Tests are currently determining whether it came from Lorsban, Diazinon — which are used to keep pests off crops — or another insecticide,

"Organophosphates are bad stuff," Klassen said.

The organic compounds work as the basis of many insecticides and herbicides. But when used at the wrong time or place, they can cause serious harm to the environment. They are toxic to aquatic invertebrates, small insects that the river’s fish feed on, said ecotoxicology scientist Michael Johnson, the coalition’s technical program manager.

The coalition tests local waterways throughout the year, and is required to sample water twice in the winter after storm events. While the Santa Fe site is generally found to be clean, it has in the past hosted three reports of pollutants, Johnson said, adding: "This is by far the most serious."

Klassen said the pesticides most likely came from an almond orchard up river from the test site.

Read the full story in Saturday's Merced Sun-Star.