Searching for a mussel solution: Montana seeks to prevent infestations plaguing other states

December 8, 2016

There is no “silver bullet” for invasive aquatic mussels.

That was the message from experts around the country dealing with impacts from zebra and quagga mussels. Infestations of the mollusks plague waterways in the Midwest, throughout the Great Lakes and the lower Colorado River, clogging infrastructure and negatively altering aquatic ecosystems.

Until recently, exotic mussels had never been detected in the Northwest, but the announcement of Montana’s first positive test for mussel larvae shook water users and managers looking for answers and developing a response.

“All these municipal water structures, intakes, boat ramps, these are all hospitable habitats for these mussels,” said Montana Fish, Wildlife and Parks spokesman Greg Lemon. “It’s not that other invasive species aren’t concerning, but the potential economic and ecological impacts from mussels are very serious.”


Invasive mussels came to North America from Eurasia in the ballast water of ships. First discovered in 1988, within a year they infested western Lake Erie and have since spread to all the Great Lakes, hundreds of inland lakes and rivers.

Zebra and quagga mussels are both about the size of a thumbnail and notorious for colonizing on hard rocks and structures, reproducing unabatedly until covering virtually all available surfaces. Exotic mussels are even known to latch onto native mussels, with the USGS documenting a native mussel with nearly 10,000 zebra mussels attached.

Once infested, invasive mussels can foul boat props, clog hydropower and irrigation infrastructure and line recreational swimming areas with sharp shells.

“There are a lot of things you have to think about once you have these mussels because they can go wherever the water goes,” said Bob Wakeman, Aquatic Invasive Species Coordinator for Wisconsin Department of Natural Resources.

Wisconsin has documented exotic mussels in nearly 300 water bodies, first appearing in the Great Lakes and transported inland attached to recreational boats. Calcium is important for mussels to grow shells, and fortunately for Wisconsin, experts believe a large portion of the state is not calcium-rich enough to support mussel infestations, Wakeman said.

Wisconsin has never done a comprehensive analysis of exotic mussels for inland lakes, he said, putting efforts toward stopping their spread.

“Wisconsin has a very active aquatic invasive species program mostly focused on prevention and containment,” he said. “We’re really focused on the pathways with the message for boaters to inspect equipment, remove plants and animals and don’t move any live fish.”

The Bureau of Reclamation operates four hydropower dams on the Lower Colorado River. In 2007, quagga mussels were discovered in Nevada’s Lake Mead. Due to their small size, officials estimate they went undetected for three to five years until water samples found larvae. By then, the infestation was established.

Mussels are now present in multiple reservoirs, typically establishing populations within five years of introduction.

“It really goes back to their high reproductive rate,” said Denise Hosler, team leader at Reclamation’s Detection Laboratory for Invasive and Native Species. “Each female can release 30,000 eggs per breeding cycle, and on the lower Colorado, we don’t have those hard winters so there are 11 breeding cycles. Do the math and there are a huge amount of eggs being released.”

The initial concern for dam operators are large concentrations of mussels clogging pipes and shell debris filtering into other dam workings. That leads to increased workloads and maintenance, but as mitigation measures continue to evolve, officials do not believe the mussels ultimately threaten the ability to provide hydropower, Hosler said.

A 2016 Great Lakes’ states economic analysis by Michigan based Anderson Economic Group LLC sought to quantify the impacts of aquatic invasive species. The study estimates the cost of monitoring and controlling zebra mussels at one hydroelectric dam at $1.2 million annually. Costs for mussel controls at water treatment plants ranged from $480,000 to $540,000.

But the bigger concern may be the impacts of invasive mussels to the ecosystem, Hosler said.

Zebra and quagga mussels function similarly in the environment and unlike any other creature.

“This organism fills a unique niche as a freshwater bivalve filtering nutrients from the water,” she said. “This one doesn’t have any natural competition.”

As plankton feeders, exotic mussels filter about a liter of water per day. The feeding process sends ripple effects through the aquatic ecosystem in two main ways.

First, the removal of plankton decreases food supplies for smaller fish, Hosler said. A lack of nutrients works its way up the food chain, with smaller or fewer bait fish available to larger fish.

Second, water clears as mussels filter. While that might initially seem like a positive impact, increasing light penetration encourages the growth of aquatic plants, altering the underwater environment.

The exact impacts of invasives versus weather on plant growth are difficult to quantify and are the subject of current research, Hosler said.

Effects from mussels vary depending on the environment and other conditions, with calcium and dissolved oxygen being the primary factors, she said. Colder climates “no doubt” slow the rate of infestations as water bodies freeze, she added.

The state of Michigan has seen rapid infestations in shallower and species-rich portions of the Great Lakes, and slower progressions in deeper colder waters, said Sarah LeSage, AIS coordinator with the Michigan Department of Environmental Quality. The state runs educational campaigns targeting recreational boats, but still hundreds of inland lakes have been infested, she said.

“Zebra mussels are the poster child for the National Invasive Species Act,” she said. “They have a profound impact and it’s widely accepted that we need to work hard to address them.”


A number of studies and pilot projects have looked at ways to control exotic mussels.

Water testing methodology and DNA analysis has improved significantly in the past decade, allowing water managers to discover mussel presence earlier in an infestation.

In closed hydropower or irrigation systems, chemicals can be used to clean pipes. Reclamation is also researching other controls in its dams, testing different coatings and using ultraviolet light to discourage mussels from attaching.

“We’ve seen some really positive effects keeping pipes clean and flowing,” Hosler said of Reclamation’s dams, adding that open water controls are much more challenging.

“There is no silver bullet — you can reduce populations but there is no eradication method.”

LeSage agreed, noting that new collaborations between state and federal agencies are only looking at ways to restore portions of fish habitat using commercial chemical mussel controls.

“Once they’re in an inland lake, there’s not a lot we can do,” she said. “Lakewide treatments are not on the table right now.”

Minnesota has seen the same impacts to aquatic life, recreation and water users, and launched a number of projects aimed at mussel controls. About 5 percent of Minnesota’s 11,000 lakes have confirmed invasive mussel infestations.

In 2000, the state drew down Lake Zumbro in an attempt to leave mussels dry. The invasives survived in the remaining water and reestablished post drawdown.

From 2011 to 2014, Minnesota officials used commercial mussel controls consisting of copper sulfate on three lakes. Mussels were later found in two of the lakes.

A biocontrol called Zequanox uses the dead cells of bacteria deadly to invasive mussels. The product is being touted as an alternative to chemicals, and Minnesota used it in Lake Christmas in 2014. The state also used copper products and potassium chloride, and will monitor to judge efficacy, said Heidi Wolf, invasive species unit coordinator for Minnesota Department of Natural Resources.

“So far we’re focused on new infestations and are not trying to go in and eradicate them where they’re infested,” she said. “Nobody has found that silver bullet, a reliable and effective zebra mussel control, but we’re definitely trying.”


By all accounts, any potential infestation in Montana is in its infancy with only a handful of larvae confirmed in Tiber Reservoir and suspected positive samples in Canyon Ferry Reservoir, upstream in the Missouri River, and the Milk River below Nelson Reservoir. The state has expedited testing to determine species and confirm suspected samples following initial positive tests in October.

Searches by detection dogs and divers have not discovered a breeding population, but state officials are operating under the assumption that adult mussels are present in the waters.

“We’re trying to take the necessary actions to keep it contained and controlled,” Lemon said. “Even if we do find adult mussels we have no idea the extent they’re established — it’s just too early to tell.”

Gov. Steve Bullock issued an executive order late last month, declaring a natural resource emergency and formulating an invasive mussel rapid response team. The move allows state officials to tap $750,000 in special funding as it investigates and responds.

Since forming, the team closed boating and dock removal on Canyon Ferry and Tiber and reached out to water users and other interested groups.

U.S. Sens. Steve Daines and Jon Tester have worked on the federal end, asking the U.S. Army Corps of Engineers to expedite funding for invasive species check stations.

Inspecting boats for invasive plants and animals and education with the “Clean, Drain, Dry” campaign has been the primary means of prevention. Now that exotic mussels have been detected in the state, officials in Montana and throughout the Northwest are considering the options.

Winter temperatures provide a reprieve from mussel reproduction as the team prepares its response. Officials plan to continue to search for adults but have not determined if the reservoirs will reopen when the ice breaks up this spring.

One proposal calls for drawing down Tiber and Canyon Ferry in an attempt to leave mussels dry, potentially killing them and aiding in detection. Lemon emphasized that those discussions are in early stages and officials are a long way from any action. Discussions with water users about downstream impacts are also ongoing but preliminary.

“It’s impossible to say at this point what (draw down) impacts might be at this point, but we understand the broad range of stakeholders this could impact,” Lemon said. “Any sort of solution we have to contain and control, we’ll certainly involve all those key stakeholders in that discussion.”