Osnuhsa Lake
Osnuhsa Lake in Brown County, Wisconsin has a water quality grade of C (Fair). Water clarity: 5.6 ft visibility. Phosphorus: 63.5 µg/L. Chlorophyll-a (algae): 9.9 µg/L. Surface area: 6 acres.
- Clarity
- 5.6 ft
- Typical in August
- 71°F
- Area
- 6 acres
- Type
- Eutrophic
- Trend
- → Stable
Next lake in Brown County
Osnuhsa Lake is a 6-acre productive, nutrient-rich eutrophic lake in Brown County, Wisconsin. Water quality is graded C based on 2 sampling years through 2025. Water clarity is declining over recent sampling years. Compared to the 1 other monitored lakes in Brown County, Osnuhsa Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-16. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 5.6 ft. Phosphorus level: 63.5 µg/L. Chlorophyll-a: 9.9 µg/L. Trophic State Index: 56.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.6 ft | Not graded |
| Phosphorus | 63.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 9.9 µg/L | Good |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Osnuhsa Lake
Compare lakeside cabins, hotels, and vacation rentals near Osnuhsa Lake in Brown County, Wisconsin — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Osnuhsa Lake
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Water Temperature
Osnuhsa Lake typically sits around 71°F at the surface in August. Summer average is about 70°F. Usually warmest in Jul (about 72°F) and coldest in May (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 62 field readings (2024–2025) via the EPA Water Quality Portal. See the full Osnuhsa Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 6 acres |
No bathymetric survey has been published for Osnuhsa Lake, so its depth is not documented here.
Fishing Osnuhsa Lake
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.8 m/yr | 2 |
| Phosphorus | → Stable | +0.63 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -4.01 µg/L/yr | 6 |
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Osnuhsa Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Georgia-Pacific Consumer ProductsGreen Bay · 4.9 mi away · NPDES WI0001848MajorRecent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #2 of 2 lakes in Brown County
Nearby Lakes With Higher Grades
Osnuhsa Lake holds Grade C. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Brown County
Frequently asked questions about Osnuhsa Lake
What is the water quality grade for Osnuhsa Lake?
- Osnuhsa Lake in Brown County, Wisconsin has a water quality grade of C (Fair). Water clarity: 5.6 ft visibility. Phosphorus: 63.5 µg/L. Chlorophyll-a (algae): 9.9 µg/L. Surface area: 6 acres.
Is Osnuhsa Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Osnuhsa Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 9.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Osnuhsa Lake?
- Osnuhsa Lake typically sits around 71°F at the surface in August, from 62 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
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Where this data comes from
79 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Oneida Nation
ONEIDA_WQX79 samples · 2020–2025
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 4500 P F ~ Phosphorus in Water by Colorimetry Automated Ascorbic Acid Method
- 4500 P E ~ Phosphorus by Ascorbic Acid
- UNKNOWN
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Fish and recreation data from Wisconsin DNR Lakes