Koonz Lake
Shawano County, WisconsinMesotrophic
On the LakeGrade rubric, Koonz Lake pulls an A: clarity at 10.8 ft and 12 µg/L of phosphorus put it in the top bracket for Wisconsin. clarity and phosphorus rate similarly, so there is no obvious single lever to pull on watershed management.
Mesotrophic conditions dominate at Koonz Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. The lake bottoms out at 40 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. At 20 acres, Koonz Lake sits below the Wisconsin median: a small water where shoreline activity has an outsized effect on water quality. Among the 27 graded lakes in Shawano County, Koonz Lake ranks 3 — in the top quartile locally.
Koonz Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. Walleye are documented at Koonz Lake, one of 4 fish species on record for the lake. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-10-07. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Good clarity, visible to about 10.8 ft. Phosphorus level: 12 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.8 ft | B |
| Phosphorus | 12 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 40 ft |
| Surface Area | 20 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Koonz Lake (14-day solunar calendar)
→ Is it safe to eat fish from Koonz Lake? (mercury & PFAS guide)
→ Koonz Lake fishing regulations (limits, seasons, special rules)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.736 m/yr | 6 |
| Phosphorus | → Stable | -0.04 µg/L/yr | 6 |
Location
County Ranking
Ranked #3 of 27 lakes in Shawano County
Nearby Lakes in Shawano County
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Washington County · Clarity: 11.8 ft
Washington County · Clarity: 12.6 ft
Walworth County · Clarity: 11 ft
Waukesha County · Clarity: 11.3 ft
Walworth County · Clarity: 20.2 ft
Kenosha County · Clarity: 10 ft
Mesotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1991. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Koonz Lake covering fish populations, stocking, water quality, and management. 1 report on file.
- 2025Koonz and Beaulieu lakes shocking survey, 2025Fisheries Survey · WI DNR · 2025 (PDF)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2025-10-07
Monitoring stations: 2