Lac Courte Oreilles Lake
Lac Courte Oreilles Lake in Sawyer County, Wisconsin has a water quality grade of A (Excellent). Water clarity: 12.2 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Maximum depth: 90 ft. Surface area: 5139 acres.
- Clarity
- 12.2 ft
- Typical in August
- 73°F
- Max depth
- 90 ft
- Area
- 5,139 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Sawyer County
Lac Courte Oreilles Lake is a 5,139-acre mesotrophic lake in Sawyer County, Wisconsin with a maximum depth of 90 feet. Water quality is graded A based on 2 sampling years through 2026. Overall water quality is improving over recent sampling years. The lake supports 6 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 1 public boat landing. Compared to the 44 other monitored lakes in Sawyer County, Lac Courte Oreilles Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-04-29. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 12.2 ft. Phosphorus level: 15 µg/L. Chlorophyll-a: 1.7 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12.2 ft | Not graded |
| Phosphorus | 15 µg/L | Good |
| Chlorophyll-a (Algae) | 1.7 µg/L | Good |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Lac Courte Oreilles Lake
Compare lakeside cabins, hotels, and vacation rentals near Lac Courte Oreilles Lake in Sawyer 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.
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Water Temperature
Lac Courte Oreilles Lake typically sits around 73°F at the surface in August. Summer average is about 72°F. Usually warmest in Aug (about 73°F) and coldest in Sep (about 70°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 17 field readings (2024–2024) via the EPA Water Quality Portal. See the full Lac Courte Oreilles Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Lac Courte Oreilles Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (114,815 cells/mL) on December 14, 2024.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 90 ft |
| Surface Area | 5,139 acres |
| Public Access | Yes |
Recreation & Access
- Lac Courte OreillesPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Lac Courte Oreilles Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 36 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Lac Courte Oreilles Lake covering fish populations, stocking, water quality, and management. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2024Lac Courte Oreilles netting and shocking survey, 2024Netting Survey · WI DNR · 2024 (PDF)
- 2023Lac Courte Oreilles spring netting survey, 2023Netting Survey · WI DNR · 2023 (PDF)
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.45 m/yr | 5 |
| Phosphorus | ↑ Improving | -1.15 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -0.21 µg/L/yr | 4 |
EPA Impairment Status
Lac Courte Oreilles Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10004082 · Official waterbody report
County Ranking
Ranked #1 of 45 lakes in Sawyer County
Nearby Lakes in Sawyer County
Frequently asked questions about Lac Courte Oreilles Lake
What is the water quality grade for Lac Courte Oreilles Lake?
- Lac Courte Oreilles Lake in Sawyer County, Wisconsin has a water quality grade of A (Excellent). Water clarity: 12.2 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Maximum depth: 90 ft. Surface area: 5139 acres.
Is Lac Courte Oreilles Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Lac Courte Oreilles Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Lac Courte Oreilles Lake?
- Lac Courte Oreilles Lake typically sits around 73°F at the surface in August, from 17 EPA Water Quality Portal field readings (2024–2024). That is a typical value for the month, not a live reading.
How deep is Lac Courte Oreilles Lake?
- Lac Courte Oreilles Lake has a maximum depth of 90 feet. The lake covers 5139 acres.
What fish are in Lac Courte Oreilles Lake?
- Fish species found in Lac Courte Oreilles Lake include Musky, Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Lac Courte Oreilles Lake is located in Sawyer County, Wisconsin.
Does Lac Courte Oreilles Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Lac Courte Oreilles Lake (clouds, ice, or an off-season gap). The most recent reading was high (114,815 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Lac Courte Oreilles Lake?
- Lac Courte Oreilles Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lac Courte Oreilles. Public access is listed as yes.
Explore Lac Courte Oreilles Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Species activity outlook by water temperature and season
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Moderate nutrients, good water quality
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Sawyer County · Grade A
Where this data comes from
1,759 measurements from 20 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Lac Courte Oreilles (Tribal)
LCOWIS_WQX1,158 samples · 2020–2024 - Wisconsin Department of Natural Resources
WIDNR_WQX601 samples · 2020–2026
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
- 10200 H ~ Chlorophyll a-b-c Determination
- Phosphorus by Colorimetry
Monitoring station identifiers (20)
- WIDNR_WQX-10037855
- LCOWIS_WQX-LCO-5
- LCOWIS_WQX-LCO-3
- WIDNR_WQX-583097
- LCOWIS_WQX-LCO-4
- WIDNR_WQX-583067
- LCOWIS_WQX-LCO-1
- WIDNR_WQX-583066
- LCOWIS_WQX-LCO-2B
- LCOWIS_WQX-LCO-2
- LCOWIS_WQX-MB-1
- LCOWIS_WQX-LCO-6
- WIDNR_WQX-583072
- WIDNR_WQX-10033577
- WIDNR_WQX-10044724
- WIDNR_WQX-583046
- WIDNR_WQX-583071
- WIDNR_WQX-10033392
- WIDNR_WQX-10037854
- LCOWIS_WQX-MB-4
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory