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LakeQuality

Grass Carp

Invasive SpeciesFound in 15 lakes

Grass Carp appears on state infested-waters lists for 15 surface waters. Boaters and anglers moving gear in or out of those lakes carry a clean-drain-dry obligation under state law. 15 lakes — narrow enough that aggressive containment is still on the table. Most upper-Midwest invasives that established here did so quietly over a decade before anyone noticed, so a low number today is not a guarantee for tomorrow.

The presence of Grass Carp does not directly change a lake's LakeGrade rubric score — the grade measures the water itself, not the species inhabiting it. But invasive presence is a meaningful adjacent signal worth reading alongside the grade.

15
Total Lakes
10
Wisconsin
4
Minnesota
1
North Dakota

Lakes with Grass Carp

LakeCountyStateGradeDepth
Geneva LakeWalworthWIA135 ft
Geneva LakeWalworthWIA135 ft
Big Cedar LakeWashingtonWIA105 ft
Big Cedar Lake-North Site-Near West BendWashingtonWIA105 ft
Oconomowoc LakeWaukeshaWIA60 ft
Oconomowoc Lake SiteWaukeshaWIA60 ft
Fowler LakeWaukeshaWIA50 ft
Okauchee LakeWaukeshaWIA90 ft
Little Cedar LakeWashingtonWIA-
Spiritwood LakeStutsmanNDA54.7 ft
Big Cedar Lake Northern Basin Deep SiteWashingtonWIB105 ft
Robinson LakeWabashaMND-
Spring LakeDakotaMNF17 ft
Nelson LakeGoodhueMNF-
Grey Cloud Slough LakeWashingtonMNF-

Frequently Asked Questions

How many lakes have grass carp?

Grass Carp has been documented in 15 graded lakes: 10 in Wisconsin, 4 in Minnesota, 1 in North Dakota.

Does grass carp affect water quality?

Invasive species can significantly affect lake ecosystems. They may alter nutrient cycling, displace native species, and change water clarity. Lakes with grass carp should be monitored for changes in water quality over time.

Invasives Found With Grass Carp

Zebra Mussel

Co-occurs in 9 lakes · 688 total

Curly-Leaf Pondweed

Co-occurs in 7 lakes · 432 total

Banded Mystery Snail

Co-occurs in 6 lakes · 363 total

Starry Stonewort

Co-occurs in 6 lakes · 99 total

Chinese Mystery Snail

Co-occurs in 4 lakes · 493 total

Rudd

Co-occurs in 4 lakes · 7 total

Source: EPA National Aquatic Resource Surveys, 2026.