Osnuhsa Lake
Brown County, Wisconsin6 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Osnuhsa Lake. Here is what has been measured.
- Eutrophic
Osnuhsa Lake in Brown County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 5.6 ft visibility. Phosphorus: 63.5 µg/L. Chlorophyll-a (algae): 9.9 µg/L. Surface area: 6 acres.
Osnuhsa Lake is a 6-acre productive, nutrient-rich eutrophic lake in Brown County, Wisconsin. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyModerate algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Osnuhsa Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Osnuhsa Lake
These are the measurements Wisconsin DNR publishes for Osnuhsa Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.6 ft. Phosphorus 63.5 µg/L. Chlorophyll-a 9.9 µg/L. TSI 56.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 63.5µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 9.9µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 56 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Osnuhsa Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Osnuhsa Lake typically sits around 67°F at the surface in September. 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.
Column height runs from this lake’s coldest month (60°F) to its warmest (72°F).
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
Surface area
6 acres
No bathymetric survey has been published for Osnuhsa Lake, so its depth is not documented here.
Stays via Stay22
Stays 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
Prices for Oct 9–11, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Follow Osnuhsa Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Osnuhsa Lake
Water Quality Trend: Stable
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening2 years
Phosphorus
Stable+0.63 µg/L/yr6 years
Chlorophyll-a
Improving-4.01 µg/L/yr6 years
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.
Nearby Lakes in Brown County
Frequently asked questions about Osnuhsa Lake
Where is Osnuhsa Lake?
- Osnuhsa Lake is a lake in Brown County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Osnuhsa Lake?
- Osnuhsa Lake in Brown County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Osnuhsa Lake?
- Osnuhsa Lake typically sits around 67°F at the surface in September, from 62 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
Explore Osnuhsa Lake across LakeQuality
Fish species and the cleanest lakes across Wisconsin
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its readings
Wisconsin's cleanest lakes, ranked on agency measurements
More lakes in Wisconsin
State Parks Near Osnuhsa Lake
Other Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Fish and recreation data from Wisconsin DNR Lakes