CODY, Wyo. (AP) — The recent discovery of damaging zebra and quagga mussels in some Montana waters has Yellowstone National Park and Wyoming Game and Fish officials becoming more vigilant in their efforts to keep the invasive species out.

"We have pushed it more with Montana finding mussels," said Greg Mayton, an aquatic invasive species specialist in the Cody regional Game and Fish office, of Wyoming's situation. "It turns Montana into a high-risk state."

Yellowstone, which is already battling nonnative lake trout in Yellowstone Lake, has ramped up awareness of the danger of invasive species in park waters.

"The bottom line, if we get aquatic invasive species in Yellowstone National Park, it will be difficult, if not impossible to remove them," park superintendent Dan Wenk said.

Starting this year, only rubber boots will be allowed in Yellowstone because felt sole boots are virtually impossible to cleanse of mussels.

"That gets embedded in the footwear," said Todd Koel, Yellowstone senior fisheries biologist.

Mussels can take over water bottoms and eat the bottom-dwelling food sources that many fish need to thrive, ultimately decimating populations.

They also spread to boat docks, anchors and buoys and become encrusted there and spread to beaches.

Watercraft inspection is a vital element in keeping invasive species out of Wyoming waters and that's why there are 45 inspectors deployed at entry points around the state.

Boats can be turned away at the border if a boat flunks inspection. But if an owner is attentive, that should not happen.

"As long as you clean your boat off and drain the water, the risk is almost zero," Mayton said.

Koel said if waters in Yellowstone become infected with mussels, "we would basically be infecting everything downstream. It's not something we can tolerate in Yellowstone."