YANKTON, S.D.(KYNT)- South Dakota’s native freshwater mussels clean the water in state rivers and streams, but agricultural pollution and habitat destruction appear to be reducing their numbers throughout South Dakota are a new threat to aquatic populations.

Experts wonder if state and federal wildlife and environmental protection agencies are doing enough to protect native freshwater mussels.

Izzak Walton League Regional Conservation Coordinator Paul Lepisto says pollution and other destruction could have major long-term cost effects

Lepisto says steps need to be taken now to improve water quality for all species, not just mussels.

Recent surveys of the state’s major river basins found only 17 of the 36 mussel species once known to live in state waters, a 53% decline.