The small, stripy-shelled critters hitch rides on boats as they’re towed from lake to lake. Once they multiply in a new body of water, they can choke out native species and stick to all kinds of surfaces.

The Oklahoma Department of Wildlife Conservation says they’ve caused millions of dollars of damage to water infrastructure and boat engines.

Over the past month, the ODWC has identified zebra mussels at Fort Supply Lake in Northwest Oklahoma and in Dave Boyer Lake in the southwestern part of the state. They’ve already been found in more than 25 other Oklahoma bodies of water.

Wildlife officials say zebra mussels are hard to get rid of once they’re in a lake. So you have to stop them ahead of time. The ODWC urges boaters to drain their bilge water and clean their watercraft before moving them from one lake to another.