St. Johns Lake
St. Johns Lake in Forest County, Wisconsin has a water quality grade of B (Good). Water clarity: 10 ft visibility. Phosphorus: 14.9 µg/L. Maximum depth: 21 ft. Surface area: 107 acres.
- Clarity
- 10 ft
- Typical in July
- 78°F
- Max depth
- 21 ft
- Area
- 107 acres
- Type
- Mesotrophic
- Trend
- ↓ Declining
Next lake in Forest County
St. Johns Lake is a 107-acre mesotrophic lake in Forest County, Wisconsin with a maximum depth of 21 feet. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is declining over recent sampling years. The lake supports 3 documented fish species including Panfish, Largemouth Bass, and Walleye. Compared to the 22 other monitored lakes in Forest County, St. Johns Lake ranks #17 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-07-06. 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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Good clarity, visible to about 10 ft. Phosphorus level: 14.9 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10 ft | Not graded |
| Phosphorus | 14.9 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near St. Johns Lake
Compare lakeside cabins, hotels, and vacation rentals near St. Johns 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 St. Johns Lake
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Water Temperature
St. Johns Lake typically sits around 78°F at the surface in July. Summer average is about 76°F. Usually warmest in Jul (about 78°F) and coldest in Mar (about 41°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 25 field readings (2024–2026) via the EPA Water Quality Portal. See the full St. Johns Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 21 ft |
| Surface Area | 107 acres |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing St. Johns Lake
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2022. 1 station on file (most recent sample 2026).
Fish Species (DNR-rated)
Water Quality Trend: ↓ Declining
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.243 m/yr | 7 |
| Phosphorus | ↓ Declining | +1.95 µg/L/yr | 3 |
County Ranking
Ranked #17 of 23 lakes in Forest County
Nearby Lakes in Forest County
Frequently asked questions about St. Johns Lake
What is the water quality grade for St. Johns Lake?
- St. Johns Lake in Forest County, Wisconsin has a water quality grade of B (Good). Water clarity: 10 ft visibility. Phosphorus: 14.9 µg/L. Maximum depth: 21 ft. Surface area: 107 acres.
Is St. Johns Lake safe to swim in?
- Good for swimming, clear water with low algae levels. St. Johns Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
What is the water temperature of St. Johns Lake?
- St. Johns Lake typically sits around 78°F at the surface in July, from 25 EPA Water Quality Portal field readings (2024–2026). That is a typical value for the month, not a live reading.
How deep is St. Johns Lake?
- St. Johns Lake has a maximum depth of 21 feet. The lake covers 107 acres.
What fish are in St. Johns Lake?
- Fish species found in St. Johns Lake include Panfish, Largemouth Bass, Walleye. St. Johns Lake is located in Forest County, Wisconsin.
Explore St. Johns Lake across LakeGrade
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Where this data comes from
64 measurements from 1 monitoring station, 2022–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX64 samples · 2022–2026
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes