YANKTON, S.D.(WNAX)- Zebra mussels, an invasive clam that attaches itself to underwater structures, is becoming more of a problem at Gavins Point Dam on the Missouri River.

Operations Manager Tom Curran says they continue to fight the sticky shells.

Curran says the mussels find their way into their cooling system.

Curran says the mussels have an indirect impact on hydropower production at the dam.

The zebra mussels are spread from lake to lake by attaching to boats that are not cleaned between launchings.