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LakeQuality
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Eurasian Watermilfoil

Invasive speciesRecorded in 792 lakes

Eurasian watermilfoil is a submerged aquatic plant that forms dense surface-canopy mats, crowding out native vegetation and limiting boat access. Documented in 792 lakes in our dataset. A 792-lake footprint means Eurasian Watermilfoil prevention has shifted from "stop the spread" to "manage the new normal." Watercraft-inspection programs at boat launches and shoreline-management practices on individual lakes are doing most of the active prevention work.

A milfoil-infested lake can still read clear on the Secchi disk, since the plant itself does not cloud the water, but recreational use is meaningfully affected, and that is not captured in the water-quality readings.

792
Lakes with records
438
Wisconsin
354
Minnesota

Lakes with Eurasian Watermilfoil

LakeCountyStateDepth
Clearwater LakeWrightMN73 ft
Clearwater LakeCrow WingMN54 ft
Little Birch LakeToddMN89 ft
North Long LakeCrow WingMN97 ft
Big LakeSherburneMN48 ft
Birch LakeRamseyMN-
Birch LakeWrightMN52 ft
Washburn LakeCassMN111 ft
Otter LakeRamseyMN21 ft
Ossawinnamakee LakeCrow WingMN63 ft
Florida LakeKandiyohiMN40 ft
Spectacle LakeIsantiMN51.5 ft
Marion LakeDakotaMN21 ft
Mantrap LakeHubbardMN-
Fish LakeChisagoMN57 ft
Snail LakeRamseyMN30 ft
Green LakeKandiyohiMN110 ft
Girl LakeCassMN81 ft
Charlotte LakeWrightMN46 ft
Leech LakeCassMN-
Bass LakeCrow WingMN27 ft
Crooked LakeCrow WingMN54 ft
Portage LakeCrow WingMN37 ft
Cedar LakeWrightMN108 ft
Turtle LakeRamseyMN28 ft
Mitchell LakeSherburneMN33 ft
Alexander LakeMorrisonMN64 ft
Henderson LakeKandiyohiMN57 ft
Minnewashta LakeCarverMN70 ft
Lawrence LakeCassMN71 ft
Courthouse LakeCarverMN57 ft
Kimball LakeCrow WingMN77 ft
Big Marine LakeWashingtonMN-
West Sylvia LakeWrightMN97 ft
Upper Mission LakeCrow WingMN36 ft
Pleasant LakeWrightMN74 ft
Pulaski LakeWrightMN-
Roosevelt LakeCassMN129 ft
Bay LakeCrow WingMN74 ft
White Bear LakeWashingtonMN83 ft
Le Homme Dieu LakeDouglasMN85 ft
Shamineau LakeMorrisonMN52 ft
Pine LakeCrow WingMN16.9 ft
Lac Lavon LakeDakotaMN32 ft
Geneva LakeDouglasMN63 ft
South Lindstrom LakeChisagoMN34 ft
Holland LakeDakotaMN55 ft
East Sylvia LakeWrightMN78 ft
O'Brien LakeDakotaMN-
Piersons LakeCarverMN40 ft

Showing 50 of 792 lakes with a record.

Frequently Asked Questions

How many lakes have eurasian watermilfoil?

Eurasian Watermilfoil is recorded in 792 measured lakes: 438 in Wisconsin, 354 in Minnesota. 792 of them carry a state infested-waters listing or an established population.

Does eurasian watermilfoil affect water quality?

An established invasive population can change how a lake works — altering nutrient cycling, displacing native species, and shifting water clarity. Clarity is the one to watch: filter-feeders can make water read clearer on a Secchi disk without any drop in nutrient loading, so a lake with eurasian watermilfoil is worth reading alongside its clarity number rather than through it.

Invasives Found With Eurasian Watermilfoil

Curly-Leaf Pondweed

Co-occurs in 255 lakes · 387 total

Banded Mystery Snail

Co-occurs in 197 lakes · 341 total

Chinese Mystery Snail

Co-occurs in 196 lakes · 469 total

Zebra Mussel

Co-occurs in 142 lakes · 609 total

Zebra Mussel

Co-occurs in 132 lakes · 609 total

Purple Loosestrife

Co-occurs in 127 lakes · 242 total

More on invasive species and lake health

Zebra Mussel Spread: How Many Lakes Are Affected?

Zebra mussel counts from the lakes LakeQuality tracks, the counties that show up most often, and the Clean, Drain, Dry rules that still matter.

Lake Water Quality Explained: What the Readings Mean

How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.

What to Check Before Buying Lakefront Property

Before you buy lakefront, check the water: clarity trend, nutrient impairment, algae advisories, invasive species, and depth — a data-backed checklist.

Source: EPA National Aquatic Resource Surveys, 2026.