Japanese Knotweed
Invasive speciesRecorded in 16 lakes
Japanese Knotweed appears on state infested-waters lists for 16 surface waters. Boaters and anglers moving gear in or out of those lakes carry a clean-drain-dry obligation under state law. 16 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 Japanese Knotweed does not change a lake's clarity, phosphorus or algae readings, which measure the water itself, not the species living in it. Invasive presence is still worth reading alongside those numbers.
Lakes with Japanese Knotweed
| Lake | County | State | Depth |
|---|---|---|---|
| Long Lake | Bayfield | WI | 28 ft |
| Deer Lake | Polk | WI | 46 ft |
| Tabor Lake | Burnett | WI | 28 ft |
| Lake Nebagamon | Douglas | WI | 56 ft |
| Big Roche A Cri Lake | Adams | WI | 20 ft |
| Springville Pond | Portage | WI | 10 ft |
| Alpine Lake | Waushara | WI | 18 ft |
| Mcdill Pond | Portage | WI | 19 ft |
| Yellow Lake | Burnett | WI | 31 ft |
| Wapogasset Lake | Polk | WI | 32 ft |
| Amherst Millpond | Portage | WI | 7 ft |
| Cedar Lake | Polk | WI | 32 ft |
| Tainter Lake | Dunn | WI | 37 ft |
| Mason Lake | Adams | WI | 9 ft |
| Balsam Lake Little Balsam Site | Polk | WI | 37 ft |
| Swan Lake | Columbia | WI | 82 ft |
Frequently Asked Questions
How many lakes have japanese knotweed?
Japanese Knotweed is recorded in 16 measured lakes: 16 in Wisconsin. 16 of them carry a state infested-waters listing or an established population.
Does japanese knotweed 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 japanese knotweed is worth reading alongside its clarity number rather than through it.
Invasives Found With Japanese Knotweed
More on invasive species and lake health
Zebra mussel counts from the lakes LakeQuality tracks, the counties that show up most often, and the Clean, Drain, Dry rules that still matter.
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.
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.