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FWP wraps up busy season fighting invasive water species

Daily Inter Lake | September 29, 2021 12:00 AM

The Montana Department of Fish, Wildlife and Parks is wrapping up another busy season working to prevent invasive mussels, snails, clams and aquatic weeds from overrunning lakes and rivers across the state.

The agency, which has its own dive team and partners with private conservation groups across Montana, has surveyed more than 300 bodies of water, collected more than 2,200 early-detection samples and reported several concerning discoveries this year.

For the first time, New Zealand mudsnails — tiny creatures that can reproduce rapidly, displace native species and disrupt food chains — were found in several of Montana's natural water bodies west of the Continental Divide, the agency said in a news release. And red-rimmed melania snails were discovered in the Gardner River as well as a warm spring near Beaverhead Rock State Park, likely introduced when a careless fish owner dumped an aquarium tank.

One success story, meanwhile, is a long-running effort to eradicate Eurasian watermilfoil in Beaver Lake, about a mile west of Whitefish Lake.

Eurasian watermilfoil is an invasive weed that can grow into thick tangles, displace native plant species and obstruct recreational activities such as fishing, swimming and boating. It was first detected near Beaver Lake's boat ramp in 2011, and eradicating it has been a priority for FWP, the Whitefish Lake Institute and the city of Whitefish due to concern that it could spread throughout the watershed.

"THE INTENT is to eradicate this stuff, and we've seen less and less every year," said Thomas Woolf, chief of FWP's aquatic invasive species bureau. "We're hopeful we can keep after it and totally eradicate it so it doesn't move downstream."

About 10 pounds of vegetation, including Eurasian watermilfoil, were pulled from Beaver Lake this year, Woolf said. Divers also placed large black tarps over patches on the bottom of the lake, which starve the weed of sunlight and eventually kill it.

This year, "there was an area near the fishing pier that had Eurasian milfoil mixed in with native plants and that was covered with barriers," Woolf said. "We will leave those barriers in all winter and will survey the lake again in the spring. The barriers will kill all the milfoil in that area."

Mike Koopal, executive director of the Whitefish Lake Institute, said it's impossible to know precisely how much Eurasian watermilfoil remains in Beaver Lake, but "it's in low densities to a point where it's manageable.

"I'm cautiously optimistic," Koopal said. "I think we're at a point where it's still up in the air whether it's going to be a control effort or a possible eradication."

In Montana, Eurasian watermilfoil also has been found in the Lower Clark Fork and Jefferson rivers and the Noxon and Cabinet Gorge reservoirs, Woolf said.

"But it's not in the Flathead Basin, which is really important, and we're trying to keep it out," he said, emphasizing the importance of FWP's watercraft inspection stations. "We're really trying to prevent the movement of things like mussels, but also Eurasian watermilfoil and some of these aquatic noxious weeds that also move on boats."

WHILE MONTANA watercraft inspectors have stopped dozens of mussel-fouled boats this year, FWP reported "no evidence" of invasive mussel populations has been found in the state's lakes and rivers this year.

Surveys are still being wrapped up for the season, but the agency said it would consider lifting inspection requirements for boats exiting Tiber Reservoir if no evidence of mussels is found in the reservoir in north-central Montana. Final sampling results should be completed by the end of October.

FWP also has worked this year to remove fragrant water lilies from Holland Lake in the Mission Mountains and eradicate Asian clams in Lake Elmo in Billings.

New Zealand mudsnails were discovered in three new locations east of the Divide, including Beavertail Pond east of Clinton, the Mitchell Slough on the Bitterroot River and Big Sheep Creek near Dell. The snails often hitch a ride to new locations by clinging to plants, muddy boots or fishing gear.

FWP also identified a new population of curlyleaf pondweed in Big Elk Creek near Two Dot in the Musselshell River drainage. The agency said curlyleaf pondweed can grow in high densities that obstruct boating and water flow for irrigation.

"These new detections are a reminder to ensure boats, trailers, fishing gear, waders and clothing are always clean and free of mud, plants and vegetation; all water is drained; and boats and gear are thoroughly dry before entering another water body," the agency said. "Aquarium pet owners should never dispose of aquarium water, plants or animals into natural waterways."

The public can report sightings of aquatic invasive species to FWP by calling 406-444-2440.

Assistant editor Chad Sokol may be reached at 406-758-4439 or