Slim Lake
Slim Lake in Washburn County, Wisconsin has a water quality grade of B (Good). Water clarity: 15.7 ft visibility. Phosphorus: 13 µg/L. Maximum depth: 42 ft. Surface area: 210 acres.
- Clarity
- 15.7 ft
- Max depth
- 42 ft
- Area
- 210 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Slim Lake is a 210-acre cold, clear oligotrophic lake in Washburn County, Wisconsin with a maximum depth of 42 feet. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is improving over recent sampling years. The lake supports 5 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 5 public boat landings. Compared to the 26 other monitored lakes in Washburn County, Slim Lake ranks #22 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-16. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyLimited data
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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Crystal clear, you can see 15.7 ft down. Phosphorus level: 13 µg/L. Trophic State Index: 39.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15.7 ft | Not graded |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 39 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Slim Lake
Compare lakeside cabins, hotels, and vacation rentals near Slim Lake in Washburn 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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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 42 ft |
| Surface Area | 210 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Slim LakePublic
- Slim Creek FlowagePublic
- Scoot LakePublic
- Osprey LakePublic
- Birchwood Fire Lane - Unnamed LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Slim 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.
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +1 m/yr | 2 |
| Phosphorus | ↑ Improving | -0.9 µg/L/yr | 4 |
EPA Impairment Status
Slim Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5R).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10004596 · Official waterbody report
County Ranking
Ranked #22 of 27 lakes in Washburn County
Nearby Lakes With Higher Grades
Slim Lake holds Grade B. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Washburn County
Frequently asked questions about Slim Lake
Where is Slim Lake?
- Slim Lake is a lake in Washburn County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Slim Lake?
- Slim Lake in Washburn County, Wisconsin has a water quality grade of B (Good). Water clarity: 15.7 ft visibility. Phosphorus: 13 µg/L. Maximum depth: 42 ft. Surface area: 210 acres.
Is Slim Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Slim Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
How deep is Slim Lake?
- Slim Lake has a maximum depth of 42 feet. The lake covers 210 acres.
What fish are in Slim Lake?
- Fish species found in Slim Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Slim Lake is located in Washburn County, Wisconsin.
Are there boat ramps on Slim Lake?
- Slim Lake has 5 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Slim Lake, Slim Creek Flowage, Scoot Lake, Osprey Lake, among others. Public access is listed as yes.
Explore Slim Lake across LakeQuality
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Where this data comes from
19 measurements from 1 monitoring station, 2021–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX19 samples · 2021–2026
Analytical methods
- Phosphorus by Colorimetry
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
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