Ecology

Zebra Mussels

Small, striped freshwater mussels native to Eastern Europe that attach to hard surfaces in lakes, filter large volumes of water, and alter lake ecosystems.

What It Means for Your Lake

Zebra mussels (Dreissena polymorpha) are small freshwater bivalves, typically 1 to 2 inches long, with distinctive dark and light striped shells. Native to the Caspian Sea region, they arrived in North America via ballast water from transoceanic ships in the late 1980s and were first detected in Lake St. Clair near Detroit. They spread rapidly through the Great Lakes and connected waterways, reaching Minnesota in the late 1990s and now infesting over 200 Minnesota lakes and rivers and numerous Wisconsin water bodies. Zebra mussels reproduce prolifically, a single female can release up to one million eggs per year, and the microscopic larvae (veligers) are easily transported in livewells, bait buckets, and water retained in boat motors and bilges. Their impact on lake ecosystems is profound and complex. Each adult zebra mussel can filter one liter of water per day, and dense colonies (sometimes exceeding 100,000 per square meter) can filter the entire volume of a lake multiple times during the summer season. This filtration dramatically increases water clarity, which sounds beneficial but actually causes a cascade of ecological changes: increased light penetration promotes nuisance growths of attached algae (Cladophora) on rocks and shorelines, native aquatic plants may expand into previously too-deep habitat, and the nutrients removed from the water column are deposited on the lake bottom as mussel waste (pseudofeces), shifting the nutrient cycle from open-water to nearshore zones. The economic impacts include fouled boat motors, damaged docks and lifts, sharp shells on swimming beaches, and clogged water intake pipes for municipalities and industries.

Frequently Asked Questions