Oyster growers in southwest Washington are preparing to spray up to 2,000 acres of commercial shellfish beds after winning state approval to use a neurotoxic pesticide to control a native burrowing shrimp.

They say it's a safe way to check a threat to the area's multi-million shellfish industry.

But critics, including the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration, worry about unintended harm to other species. They say there are too many unknowns about the pesticide's effects.

The state Department of Ecology approved the permit two weeks ago. The agency says it has enough information and that the pesticide is less toxic than the one it's replacing. It says monitoring will be required to ensure that there aren't significant harmful effects.