PERRYVILLE, Mo. (AP) — The U.S. Fish and Wildlife Service will add a small, cave-dwelling fish found only in one southeast Missouri county to the list of endangered species.

But the agency’s decision on Tuesday did not declare the grotto sculpin’s habitat in Perry County “critical habitat,” meaning no protection measures will be required.

Instead, the service will rely on a voluntary conservation plan developed by federal, state and Perry County officials. It includes specific plans for improving water quality in the fish’s habitat.

The grotto sculpin lives in area of Perry County that has hundreds of caves and thousands of sinkholes. It is threatened by water contaminated by agricultural runoff and other pollutants.

The listing as an endangered species takes effect Oct. 25.