South Bay Lake
South Bay Lake in Forest County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 12 ft visibility. Maximum depth: 46 ft. Surface area: 839 acres.
Wisconsin DNR lists Panfish as common on South Bay Lake. DNR survey details →
- Clarity
- 12 ft
- Max depth
- 46 ft
- Area
- 839 acres
- Trend
- ↓ Declining
- Public access
- Yes
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Why South Bay Lake has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For South Bay Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by WI DNR and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
South Bay Lake is a 839-acre lake in Forest County, Wisconsin with a maximum depth of 46 feet. Overall water quality is declining over recent sampling years. The lake supports 5 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-21. Grade methodology: LakeQuality methodology.
Watch South Bay Lake water quality
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for South Bay Lake
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 12 ft. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near South Bay Lake
Compare lakeside cabins, hotels, and vacation rentals near South Bay 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 South Bay Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for South Bay Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (554,626 cells/mL) on November 22, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Panfish as common on South Bay Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality does not assign an A–F grade on South Bay Lake — official chemistry is on file, not a letter, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1986. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 46 ft |
| Surface Area | 839 acres |
| Public Access | Yes |
Fish Species
Click a species to see every graded lake where it is documented.
Fishing South Bay 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: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.086 m/yr | 6 |
| Phosphorus | ↓ Declining | +2.53 µg/L/yr | 6 |
Graded lakes near South Bay Lake
South Bay Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Forest County
Frequently asked questions about South Bay Lake
Where is South Bay Lake?
- South Bay Lake is a lake in Forest County, Wisconsin. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for South Bay Lake?
- South Bay Lake in Forest County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 12 ft visibility. Maximum depth: 46 ft. Surface area: 839 acres.
Is South Bay Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. South Bay Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
How deep is South Bay Lake?
- South Bay Lake has a maximum depth of 46 feet. The lake covers 839 acres.
What fish are in South Bay Lake?
- Fish species found in South Bay Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. South Bay Lake is located in Forest County, Wisconsin.
What did the DNR fisheries survey find at South Bay Lake?
- Wisconsin DNR lists Panfish as common on South Bay Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality does not assign an A–F grade on South Bay Lake — official chemistry is on file, not a letter, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Does South Bay Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for South Bay Lake (clouds, ice, or an off-season gap). The most recent reading was high (554,626 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Explore South Bay Lake across LakeQuality
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Where this data comes from
41 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX41 samples · 2020–2025
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