Lake Health & Invasive Species

Wisconsin laws require boaters and anglers to take specific actions to prevent the introduction and spread of aquatic invasive species and fish diseases:

• INSPECT your boat, trailer, and equipment.
• REMOVE attached aquatic plants or animals before launching and after loading.
• DRAIN all water from boats, motors, bilges, live wells, and equipment.
• NEVER MOVE live fish away from a waterbody.
• DISPOSE of unwanted bait in the trash.
• BUY minnows from a certified Wisconsin bait dealer.

📄 Download Decontamination Best Management Practices (PDF)

🌐 Learn more about equipment disinfection on the Wisconsin DNR website.

Zebra mussels are small, non-native freshwater bivalves native to Eastern Europe. Characterized by dark, zig-zag striped shells, they average about one inch in length.

Zebra mussels filter vast amounts of water (up to a liter per day), depleting microscopic algae that form the base of the food chain for native species. They attach in dense clusters to water intake pipes, docks, and native clam shells, severely impacting ecosystems and infrastructure.

Purple loosestrife is a wetland invader that displaces native vegetation and degrades wildlife habitat. A single mature plant can produce over 2.7 million seeds annually.

Wisconsin law prohibits the sale, distribution, or planting of non-native purple loosestrife. Small infestations can be controlled manually, while larger stands are managed using biological controls like Galerucella beetles provided through the DNR.

Aquatic Invasive Plants: Invasive species like Eurasian watermilfoil disrupt native plant communities and impair recreational boating. 📄 View NR40 Regulated Aquatic Invasive Plants Handout (PDF)

Terrestrial Invasive Plants: Terrestrial weeds threaten shoreline forests and parks. 📄 View NR40 Regulated Terrestrial Invasive Plants Handout (PDF)

Harmful algal blooms (blue-green algae) occur when excessive nutrients (nitrogen and phosphorus) combine with sunlight and slow-moving water. Certain blooms produce toxins harmful to humans, pets, and wildlife.

Stay out of the water if it:

• Looks like green pea soup, green paint, or scum
• Has bright green, blue, brown, or reddish discoloration
• Emits a strong, unpleasant odor

Oak wilt is a destructive fungal disease (Ceratocystis fagacearum) affecting oak trees, particularly species in the red oak group. The fungus clogs water-conducting vessels, causing rapid leaf wilting and tree death.

Prevention Rule: Avoid pruning, cutting, or wounding oak trees between April and October to prevent sap-feeding beetles from spreading the fungus. If pruning is required during warm months, immediately seal wounds with tree wound paint.

Starry stonewort is a submerged macroalga that forms dense, monotypic mats capable of choking out native vegetation and destroying fish spawning habitat.

It is identified by distinctive star-shaped white structures called "bulbils" (3–6 mm wide) produced along rhizoids. Clean boats thoroughly to prevent introducing this alga into uninfested waters.

Emerald Ash Borer (Agrilus planipennis) is an invasive wood-boring beetle native to Asia that attacks and kills native ash tree species. Larvae feed under the bark, disrupting water and nutrient transport.

Do not transport firewood across county lines to help slow the spread of EAB to uninfested forest lands.