There’s a new aquatic invasive species on the watch-list for boaters looking to enter Montana waterways this year. 

Montana Fish, Wildlife and Parks announced on Wednesday that golden mussels have been added to the state’s invasive species list, which prohibits the possession and transport of the creature in the state. 

The species comes from Eastern Asia and was first identified in North America in California in the fall of 2024. Their distribution now ranges from San Diego to Rio Vista, according to FWP, and the first golden mussel-infested boat seen outside of California was intercepted by officials in Oregon this month.

“This illustrates the new threat of this species expanding rapidly throughout California,” FWP Aquatic Invasive Species Bureau Chief Tom Woolf said in a statement. “It’s more important than ever to ensure watercraft are inspected when they enter the state and all boats are cleaned, drained and dry when they leave the water.”

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Until this week, two primary threats to Montana waterways came from zebra and quagga muscles, bivalved molluscs that filter plankton out of the water, which can affect the food chain of native fish. 

Mussels can form dense colonies that clog water intakes affecting power plants, utilities and irrigators, and can attach to boat motors and hulls reducing the performance and efficiency of boats. 

Both quagga and zebra mussels are found throughout the eastern and midwestern U.S., with Quagga mussels also present in California, Arizona, Nevada, Utah and most recently in Idaho. While there have been detections of mussel larvae in two Montana reservoirs, the state has had a robust response, and the state is considered free of the species. 

All aquatic invasive species can create long-term ecological harm to Montana’s waterways, impacting natural resources, recreational opportunities and the economy. 

A report from the University of Montana’s Flathead Lake Biological Station estimates that if mussels colonized all of Montana’s waterways, it could cost up to $731 million in mitigation, lost revenue and property value losses. 

To prevent the spread of mussels in Montana, FWP and partner agencies manage check stations throughout the state. 

So far in 2026, FWP watercraft inspectors have checked more than 2,000 watercraft, according to the department, and found seven that were mussel-fouled. 

The infested boats were last launched in Lake Oolaga in Oklahoma, Lake Mohave and Lake Havasu in Arizona, the St. Croix River in Wisconsin, and Lake Michigan in Illinois. 

All watercraft, motorized and nonmotorized, are required to stop at all watercraft inspection stations they encounter. A map of inspection stations can be found online at FWP’s aquatic invasive species site.

FWP officials remind all boaters and other water recreationists to follow the rules to prevent aquatic invasive species from affecting Montana’s waters.

Those rules include:

• All boats must stop at all open watercraft inspection stations they encounter. Failure to do so could result in a fine of up to $700. 
• Always be sure to clean, drain and dry your boat.
• All watercraft entering Montana are required to be inspected for aquatic invasive species. An inspection is required before launching on Montana waters.
• Nonresidents transporting watercraft into Montana must purchase a Vessel AIS Prevention Pass before launching. The fee is $30 for motorized and $10 for nonmotorized watercraft. The pass is valid until Dec. 31.
• Inspection is required for Montana residents before launch IF: the boat is entering the state, crossing west over the Continental Divide or entering the Flathead basin. 

In 2025, the Montana Legislature passed a law nearly doubling the fines for failing to stop at watercraft check stations to $700 and $1400 for first and subsequent offenses.