Devil'S Lake
Devil'S Lake in Forest County, Wisconsin has a water quality grade of A (Excellent). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2.5 µg/L.
- Typical in August
- 53°F
- Mean depth
- ~17 ft est.
- Type
- Mesotrophic
- Trend
- ↓ Declining
Next lake in Forest County
Devil'S Lake is a mesotrophic lake in Forest County, Wisconsin with an estimated average depth of about 17 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Compared to the 22 other monitored lakes in Forest County, Devil'S Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-10-22. Grade methodology: LakeGrade methodology.
Watch Devil'S Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyBacteria A
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.
Based on E. coli testing, Devil'S Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 12 samples across 5 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Wisconsin’s current beach and health-department advisories before swimming.
Water Quality Grade: A (Excellent)
No clarity data. Phosphorus level: 22 µg/L. Chlorophyll-a: 2.5 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 22 µg/L | Good |
| Chlorophyll-a (Algae) | 2.5 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Devil'S Lake
Compare lakeside cabins, hotels, and vacation rentals near Devil'S Lake in Forest 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 Devil'S Lake
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 →
Water Temperature
Devil'S Lake typically sits around 53°F at the surface in August. Summer average is about 53°F. Usually warmest in Jul (about 55°F) and coldest in Apr (about 46°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 80 field readings (2024–2025) via the EPA Water Quality Portal. See the full Devil'S Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~17 ft est. |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Wisconsin has not published bathymetry for Devil'S Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Devil'S Lake
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +1.04 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.43 µg/L/yr | 6 |
County Ranking
Ranked #4 of 23 lakes in Forest County
Nearby Lakes in Forest County
Frequently asked questions about Devil'S Lake
What is the water quality grade for Devil'S Lake?
- Devil'S Lake in Forest County, Wisconsin has a water quality grade of A (Excellent). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2.5 µg/L.
Is Devil'S Lake safe to swim in?
- Based on E. coli testing, Devil'S Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 12 samples across 5 seasons. That works out to a bacteria swim-safety grade of A — a historical summary of past testing, not a current reading. Devil'S Lake has a water quality grade of A (Excellent). Bacteria levels can spike quickly after heavy rain, so always check Wisconsin's current beach and health-department advisories before you swim.
What is the water temperature of Devil'S Lake?
- Devil'S Lake typically sits around 53°F at the surface in August, from 80 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Devil'S Lake?
- No published bathymetric survey covers Devil'S Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 17 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Devil'S Lake across LakeGrade
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in Forest County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Northwoods Wisconsin area
Where to stay at Wisconsin's top lakes, each with its grade
Lakes in the Wolf River Watershed, ranked by water quality
Moderate nutrients, good water quality
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
Where this data comes from
80 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Forest County Potawatomi Community (Tribal)
FCPOTAWATOMI_WQX80 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
- 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
Lake size & watershed from HydroLAKES (HydroSHEDS)