Zebra Mussels in Montana

Zebra mussels. Photo courtesy U.S. Fish & Wildlife Service

Since their introduction to the Great Lakes in 1986 from ships’ ballast water, zebra and quagga mussels have quickly spread and are now found in over 40 states and 3 Canadian provinces. Alaska, Hawaii, Washington, Oregon, Idaho, and Wyoming are the only states to remain free of these invasive mussels.

In the fall of 2016, invasive mussel larvae were detected in Montana water bodies east of the Continental Divide. When established, zebra and quagga mussels often cause crashes in fish populations, reduce water quality, cause toxic algae blooms, cover the beaches with sharp shells, and impact native species.

Zebra and quagga mussels greatly reduce ecotourism and property values near the water, increase personal costs to clean and maintain fishing boats and gear, clog pipes (in domestic, municipal, agricultural, and hydroelectric facilities), as well as increase the costs of electricity and water due to service providers’ annual maintenance costs.

Invasive mussels on boat motor. Photo courtesy National Park Service
AIS Watercraft Inspection Sign at Whitefish Lake. Photo courtesy Nicky Ouellet, Montana Public Radio

The primary cause for zebra and quagga mussel’s movement westward is boats trailered by the public or by commercial haulers. Zebra and quagga mussels can spread on boat hulls, in water (as microscopic larvae) and on aquatic plants. A female zebra mussel can release up to one million eggs each season so transporting just one zebra mussel can spell trouble for Montana waters and your watercraft. And remember, IT IS ILLEGAL to transport zebra mussels and other invasive species into any Montana waterbody – even if it is by accident.


Progression of zebra mussel distribution in the U.S. Maps courtesy United States Geological Survey

Return to Chapter 6 Table of Contents