The confirmation of zebra mussels at Lake Ashtabula near Valley City is a near worst-case scenario for the lake, according to Jessica Howell, aquatic nuisance species coordinator for North Dakota Game and Fish Department.

"You never, ever want a zebra mussel finding," she said, "but, unfortunately, that came last week at Lake Ashtabula."

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Lake Ashtabula is a 5,200-acre lake formed by Baldhill Dam on the Sheyenne River north of Valley City.

Previously, zebra mussels had been reported in some Minnesota lakes and the Red River. The species had never been confirmed in a lake within North Dakota.

Zebra mussels can reduce fish numbers but also attach to hard surfaces in the water, damaging things like docks, dam control structures and even the cooling system of boat engines, Howell said.

James Dixon, dam manager for the U.S. Army Corps of Engineers at Pipestem Dam, said the corps is always vigilant for zebra mussels but will step up those efforts in this area.

"There is a lot of concern because of the damage they can do to waterworks," he said. "In some extreme cases, they can completely shut off pipes and the ability to move water."

Preventing the spread of the species to other lakes in the area is now the priority for North Dakota Game and Fish as well.

We try to do all we can to prevent the spread," said B.J. Kratz, fisheries supervisor for southeast North Dakota with North Dakota Game and Fish. "In the end, every person has to be diligent."

The types of behavior that can spread zebra mussels to other waters are already illegal in North Dakota.

"If people follow the law, the risk is low of the species spreading," Howell said. "People need to remove all vegetation from the boat, drain the water (live wells, etc.) and not import bait from areas where zebra mussels are."

Howell said there will be increased enforcement by game wardens at all lakes in the state this summer. Also, seasonal employees with the Game and Fish Department will be at Lake Ashtabula for the rest of the summer with an emphasis on educating the public on the threat.

People should treat all lakes as if infected with zebra mussels and clean equipment when moving from lake to lake, she said.

Howell said the damage zebra mussels do to the ecology of a lake varies and is hard to predict. In the case of Lake Ashtabula, it may vary from year to year depending on the volume of water moving through the lake from the Devils Lake outlet.

"They filter the water," she said, referring to the actions of the small mollusk. "They remove the algae the fish rely on."

The presence of zebra mussels also increases plant life in the lake and could increase algae blooms.

"They could hurt fishing but that is harder to predict," Howell said. "There likely will be some impact on fishing."

According to the U.S. Geological Survey, zebra mussels are native to Europe and Asia and likely arrived in North America in the 1980s in the bilge water of ships that called on ports in the Great Lakes. It has spread to a number of states in the region and as far away as Texas.

Howell said it is impossible to determine how the species got into Lake Ashtabula. She did estimate that the initial introduction of the zebra mussels to the lake occurred about two years ago. Biologists placed the age of some of the samples recently collected to be about 18 months old.

She also urged the public to report any possible zebra mussels that they encounter on any of the lakes or streams in North Dakota.

"There are a lot more people on the water than we have staff," Howell said.