There is a mass of weeds clogging up the boat slips nearest to shore at Bill Hinrich’s Rock Creek Marina at Fort Peck Reservoir.
“It’s worse than it’s ever been,” Hinrich said. “It’s bad enough that you can’t use those slips.”
The weed is Eurasian watermilfoil, a fast-spreading invasive species that was first discovered below Fort Peck Reservoir in 2010. In just two years, it has rapidly colonized at nearly 70 sites across the 134-mile-long lake.
Last month, the Army Corps of Engineers got help testing out two herbicides to see if the weed could be knocked back in heavily used places like Hinrich’s marina, recreation areas and near private docks. The project was coordinated by Patricia Gilbert, a natural resource specialist with the Corps in Fort Peck.
Gilbert said the herbicide application went well on the three test plots. Now she’ll wait about six to eight weeks to determine the results.
Application of the herbicides is different at every location because it’s affected by such factors as the turbidity of the water, wind and fluctuating lake levels. To help out with the design and application, Gilbert called in the Corps’ Engineering Research and Development Center, which has several decades of experience on the subject. The process, which required extensive monitoring after the application, was expensive, Gilbert said.
“The bottom line is that it would take all of the money in the world, which we don’t have, to treat the whole lake,” she said.
So any future applications of the herbicides will be directed to specific recreation areas on the lake.
“Eradication isn’t a good term to use when talking about Fort Peck,” said Dave Burch, noxious weed coordinator for the Montana Department of Agriculture, which has been involved in the project. “Control, maintenance and containment will be the goal.”
There is nothing good about Eurasian watermilfoil, Burch said. When it first takes root, it can provide habitat for small fish. But once it gets thick it creates a monoculture, choking out all native vegetation. In some places, the weed has grown so thick that people have drowned while struggling to swim through the plants.
Eurasian watermilfoil was first detected in Montana in Noxon Reservoir in 2007, probably brought in on a boat from Washington or Idaho. It can live seven to 10 days out of water in a moist spot. The northwestern Montana lake now has 400 acres infected by Eurasian watermilfoil. Almost half of that infestation was sprayed this year with good results, Burch said.
The problem is that the plant can spread so easily. In the fall, it breaks up into small pieces that are carried by the waves and water to new areas where it can colonize.
“Just trying to boat from one area to another your prop is causing that plant to fragment as well,” Gilbert said.
Waterfowl can also carry the plant to new water bodies, as can boats, boat trailers and even fishing gear. The state has aggressively stepped up its campaign to inspect, clean and dry all boats, trailers and fishing gear to help stop the spread of Eurasian watermilfoil and other aquatic invasive species.
So far, the effort has paid off. Burch said one inspection crew at Canyon Ferry this summer found a boat that had been in Fort Peck and was carrying live Eurasian watermilfoil.
“So we do know it travels a long way,” he said.
Inspections along the Yellowstone River, as well as along the shore of Tiber, Nelson and Fresno reservoirs, didn’t turn up any new infestations this year. The only other spots where the plant has been found is in Cabinet Gorge Reservoir and in a Jefferson River slough near Cardwell.
Burch theorizes that when reservoir water levels drop in the winter at places like Canyon Ferry, any Eurasian watermilfoil that is left high and dry is dying — at least he hopes so. That’s because the plant has to live in fairly shallow water — no more than 25 to 30 feet deep. In Fort Peck, it’s mostly been confined to areas about 15 feet deep.
Hinrichs, of Rock Creek Marina, said he and other lake residents have pulled the weeds with rakes and even crafted a sickle that was towed by a pontoon boat to mow the weeds down.
“That really doesn’t solve the problem, though, because all it does is leave it in the water to spread somewhere else,” Hinrichs said.
He did find one bright side to the weed infestation.
“I’ve been finding the weed beds and fishing alongside them and doing pretty good,” he said.