When Tom Millett, a Republican state lawmaker from Marion, was working at a nuclear powerplant on Lake Michigan nearly 30 years ago, he routinely found himself face to face with zebra mussels.

The small freshwater mollusks are not native to North America, but were introduced into many waterways east of the Mississippi River in the 1980s, including the Great Lakes and have spread prolifically, earning a moniker as one of the most dangerous invasive species on the continent. 

For Millett, zebra mussels would routinely coat parts of the power plant that connected to the freshwater lake.

“We had to go in there and we had to actually physically remove the zebra mussels all the time,” Millett said. “And I can just tell you stories about zebra mussels, that we would take them out in big, huge dumpsters. By the dumpster load. That’s how prolific these things are.”

In an 2024 environmental review for the Palisades Nuclear Plant on Lake Michigan, it was reported that zebra mussels still coated parts of the intake system, an inch-and-a-half thick. 

To prevent a similar problematic infestation of Montana waterways, Millett carried House Bill 242 during the 2025 Legislative session, increasing the fines for anyone who knowingly or negligently introduces any aquatic invasive species into Montana or fails to stop at a watercraft check station.

Republican Gov. Greg Gianforte signed the bill on May 5. 

Aquatic invasive species include plants, animals and pathogens that are not native to the state, and can harm the ecosystem and economy. 

Mussels are one of the common poster species for AIS prevention. 

Montana doesn’t yet have a major problem with Zebra mussels, or the similarly invasive quagga mussel, but neighboring states do, and there have been several suspicious detections of mussels and their larvae in Montana waterways, including Canyon Ferry Reservoir and the Missouri River. 

Montana Fish Wildlife and Parks runs a program to counteract aquatic invasive species, which includes a public information campaign and numerous AIS check stations that all boaters in Montana, including non-motorized ones such as canoes and stand-up paddleboards, are required to stop at for inspection. 

Out-of-state boaters must also obtain an inspection before launching on Montana waters. 

In 2024, FWP officials reported intercepting more than 47 mussel-fouled boats, and 800 transporting aquatic weeds. 

According to the state’s AIS inspection dashboard, FWP reports that watercraft check stations have already intercepted 10 mussel-fouled boats in 2025. 

The new law essentially doubles the fine for a first negligent offense as well as subsequent offenses for introducing AIS or failing to stop at an inspection station— from $500 to $700 for a first offense and from $750 to $1400 for subsequent offenses. 

In addition, knowingly attempting to introduce an invasive species to Montana, a felony, now has a fine of as much as $25,000. 

“Is that tough? It’s absolutely tough, because we can’t risk having AIS being introduced into Montana to hurt our fishing industry, our tourism industry, our hydro facilities, our water treatment plants or any of our industries that employ thousands of Montanans,” Millett said during a hearing on his bill in February. “We need to send a message to everyone who wants to come to Montana that we are serious about keeping our waters clean now and for future generations.”

Millett’s bill was supported during legislative hearings by researchers with the Flathead Lake Biological Station, the Montana Association of Conservation Districts, Montana Audubon, The Fishing Outfitters Association of Montana, Trout Unlimited, and the Little Bitterroot Lake Association. 

The threat of AIS, specifically zebra and quagga mussels, comes with a drastic price tag. 

A 2019 study published by the University of Montana’s Flathead Lake Biological Station estimated that if mussels colonized all of Montana’s water bodies, it could cost the state between $384.5 million to $731.4 million in mitigation costs, lost revenue and property value losses.

Prevention efforts, by comparison, are cheap. 

Montana spent more than $3.6 million running its inspection and decontamination stations in 2018, and operates a grant program that disseminates more than a half million dollars for invasive species-related prevention. 

In 2024, the Fish, Wildlife and Parks and partners conducted more than 130,000 watercraft inspections across the state, resulting in 47 citations and 91 written warnings. 

Under the law signed last week, the increased fines leveraged against violators would be funneled into the state’s general fund. 

FWP officials remind all Montanans that boaters and anglers must remember to clean, drain and dry their watercraft before leaving a water access site and are required to stop at all open watercraft inspection stations. 

Nonresidents and residents returning home must have their watercraft inspected before launching in Montana. Watercraft must also be drained of all water before transporting.  

For more information, visit fwp.mt.gov/conservation/aquatic-invasive-species or www.cleandraindrymt.com.