Purple Loosestrife
Invasive SpeciesFound in 275 lakes
Purple Loosestrife appears on state infested-waters lists for 275 surface waters. Boaters and anglers moving gear in or out of those lakes carry a clean-drain-dry obligation under state law. At 275 infested lakes, Purple Loosestrife is past the "containable" stage in the upper Midwest — every public boat-launch on uninfested water should now assume incoming boaters may be carrying it.
The presence of Purple Loosestrife does not directly change a lake's letter grade — the grade measures the water itself, not the species living in it. Invasive presence is still worth reading alongside the grade.
Lakes with Purple Loosestrife
| Lake | County | State | Grade | Depth |
|---|---|---|---|---|
| Green Lake | Green Lake | WI | A | 236 ft |
| Lake Beulah | Walworth | WI | A | 58 ft |
| Okauchee Lake | Waukesha | WI | A | 90 ft |
| Powers Lake | Kenosha | WI | A | 33 ft |
| Big Sand Lake | Burnett | WI | A | 55 ft |
| Osprey Lake | Sawyer | WI | A | 32 ft |
| Gaslyn Lake | Burnett | WI | A | 12 ft |
| Wind Lake | Polk | WI | B | 7 ft |
| Boulder Lake | Vilas | WI | B | 23 ft |
| Spider Lake | Vilas | WI | B | 43 ft |
| Pickerel Lake | Oconto | WI | B | 10 ft |
| Beaver Dam Lake | Barron | WI | B | 106 ft |
| Balsam Lake | Polk | WI | B | 37 ft |
| Silver Lake | Kenosha | WI | B | 44 ft |
| Silver Lake | Waukesha | WI | B | 40 ft |
| Silver Lake | Vilas | WI | B | 19 ft |
| Mirror Lake | Waupaca | WI | B | 43 ft |
| Ashippun Lake | Waukesha | WI | B | 35 ft |
| Kusel Lake | Waushara | WI | B | 29 ft |
| Spencer Lake | Waupaca | WI | B | 53 ft |
| Little Spider Lake | Vilas | WI | B | 23 ft |
| Bone Lake | Polk | WI | B | 43 ft |
| Ottawa Lake | Waukesha | WI | B | 16 ft |
| Bear Lake | Oneida | WI | B | 20 ft |
| Bear Lake | Barron | WI | B | 87 ft |
| Bear Lake | Waupaca | WI | B | 62 ft |
| Long Lake | Waupaca | WI | B | 76 ft |
| Long Lake | Bayfield | WI | B | 28 ft |
| Long Lake | Burnett | WI | B | 41 ft |
| Long Lake | Fond du Lac | WI | B | 47 ft |
| Long Lake | Waushara | WI | B | 71 ft |
| Crooked Lake | Oconto | WI | B | 37 ft |
| Rush Lake | Winnebago | WI | B | 5 ft |
| Rock Lake | Kenosha | WI | B | 33 ft |
| North Lake | Waupaca | WI | B | 33 ft |
| Red Cedar Lake | Barron | WI | B | 53 ft |
| Red Cedar Lake | Jefferson | WI | B | 6 ft |
| Lake Galilee | Ashland | WI | B | 23 ft |
| Pewaukee Lake | Waukesha | WI | B | 45 ft |
| Shadow Lake | Waupaca | WI | B | 41 ft |
| High Lake | Vilas | WI | B | 36 ft |
| Camelot Lake | Adams | WI | B | 24 ft |
| Stone Lake | Washburn | WI | B | 49 ft |
| Island Lake | Rusk | WI | B | 54 ft |
| Island Lake | Oneida | WI | B | 26 ft |
| North Twin Lake | Polk | WI | B | 27 ft |
| Lake Emily | Portage | WI | B | 35 ft |
| Big Lake | Polk | WI | B | 24 ft |
| Reisner Lake | Florence | WI | B | 5 ft |
| Kentuck Lake | Vilas | WI | B | 40 ft |
Showing 50 of 275 infested lakes.
Frequently Asked Questions
How many lakes have purple loosestrife?
Purple Loosestrife has been documented in 275 graded lakes: 275 in Wisconsin.
Does purple loosestrife affect water quality?
Invasive species can significantly affect lake ecosystems. They may alter nutrient cycling, displace native species, and change water clarity. Lakes with purple loosestrife should be monitored for changes in water quality over time.
Invasives Found With Purple Loosestrife
Co-occurs in 164 lakes · 420 total
Co-occurs in 144 lakes · 494 total
Co-occurs in 102 lakes · 362 total
Co-occurs in 85 lakes · 247 total
Co-occurs in 72 lakes · 667 total
Co-occurs in 20 lakes · 95 total
More on invasive species and lake health
Zebra mussel counts from the lakes LakeQuality grades, the counties that show up most often, and the Clean, Drain, Dry rules that still matter.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.
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.