Courtesy IPAMS
Eurasian watermilfoil (Myriophyllum spicatum L.) was discovered in two places — nearly 700 miles apart — on the Missouri River, state officials said. The plant was found at Toston Dam and at Fort Peck Dam and in the Jefferson River near Three Forks. The milfoil is classified as a Priority 1B noxious weed in Montana. The nonnative aquatic plant from Europe and Asia will, if unchecked, cover a water body with a thick, impenetrable mat that interferes with boating, swimming, fishing and other activities. Growing completely underwater, with only the inflorescences above the water’s surface, it can often be difficult to notice in early stages. Once mature, it forms a dense canopy, like that shown in this photo. Ecologically, it suppresses native plants and changes the equilibrium between predator fish and their prey. The weed costs millions of dollars a year to manage in the U.S., and even more in other economic losses. For more information, visit IPAMS – the Invasive Plant Atlas of the Mid-South at Mississippi State University.
By Michael Tucker, staff writer
A summer-long push by a task force formed to tackle and track Eurasian watermilfoil has determined the troublesome aquatic weed is not in the Madison and Gallatin rivers.
The presence of the noxious weed in the Jefferson River near Three Forks likely resulted from someone dumping a fish aquarium in a tributary stream, a consultant working with the state said.
Likely source was aquarium dumped in creek
Milfoil was found in the Missouri River drainage at For Peck Dam and at Toston Dam last year, according to the Montana departments of Agriculture and Fish, Wildlife and Parks. The scourge was also detected in several places in the Jefferson River at that time.
A task force of government agencies starting mapping the weed to determine its reach, said Celestine Duncan, a weed consultant working for the Montana Department of Natural Resources and Conservation.
In severe infestations, milfoil can stop all forms of recreational activity on bodies of water due to the dense mats it forms. The scourge can break apart and easily form new colonies. Milfoil can be dried up for up to seven days but be revived once it hits water again.
Agencies can’t say for sure, but officials are pointing to the Jefferson Slough as the source of the infestation, Duncan said. The 11-mile-long slough runs between Whitehall and Cardwell. A tributary stream, Whitetail Creek, flows into the slough and could be the sourcepoint.
Typically, the aquatic weed is carried in by motorized boats, but this case could stem from someone dumping an aquarium into the creek, Duncan said.
“Eurasian watermilfoil used to be a pretty common aquarium plant,” she said. “People get tired of their aquariums and go out back and dump it in the creek. That may have been what started it in the Jefferson Slough. That’s what it looks like.”
Surveyors could not find the noxious weed in any of the lakes or reservoirs above the Jefferson Slough, which led to more investigation of the slough, Duncan said. Whitetail Creek is the main tributary, but other potential sources, such as sewage lagoons and other sloughs will be inspected further.
“We still have to do some checking to find out for sure, but at the moment, that looks like the source,” she said of a potential aquarium dumping in Whitetail Creek. “It’s going to take awhile because it’s a convoluted drainage system.”
The good news is that blue-ribbon streams like the Madison, West and East Gallatin rivers are free and clear of the noxious weed. But surveyors did find a different aquatic weed, curlyleaf pondweed there, as well as in the Jefferson River, Hebgen and Ennis lakes and along the Missouri River to Fort Peck.
Curlyleaf pondweed has the same ranking as Eurasian watermilfoil on the state noxious weed list, but it isn’t as prevalent as milfoil, Duncan said.
“It doesn’t have the same status in terms of where we are finding it and the impacts it has on aquatic plant communities,” she said. Pondweed is more prevalent on both sides of the divide, but the plant goes dormant in the summer when water temperatures rise, Duncan said.
“It’s never had the impact or the potential impact of Eurasian watermilfoil,” she said.
Diving crews have been working to remove milfoil from Toston Dam, Duncan said. Once the Jefferson Slough has been further studied, the task force will form a plan to address the infestation.