South Twin Lake
South Twin Lake in Polk County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 11.7 µg/L. Maximum depth: 9 ft. Surface area: 72 acres.
- Max depth
- 9 ft
- Area
- 72 acres
- Trend
- → Stable
- Public access
- Yes
Next lake in Polk County
Why South Twin Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: 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 Twin Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded phosphorus, but not water clarity 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 Twin Lake is a 72-acre lake in Polk County, Wisconsin with a maximum depth of 9 feet. Water clarity is declining over recent sampling years. The lake supports 3 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-27. Grade methodology: LakeGrade methodology.
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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 Twin Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
No clarity data. Phosphorus level: 11.7 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 11.7 µg/L | Not graded |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near South Twin Lake
Compare lakeside cabins, hotels, and vacation rentals near South Twin Lake in Polk 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 | 9 ft |
| Surface Area | 72 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- South Twin LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing South Twin 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: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.226 m/yr | 5 |
| Phosphorus | ↑ Improving | -15.92 µg/L/yr | 4 |
Reservoir Info (USACE NID)
South Twin Lake is a man-made reservoir impounded by the Amery (completed 1888), built primarily for recreation on the Apple River; gravity-type dam, 13 ft tall and 190 ft long.
- Surface area
- 639 ac
- Normal storage
- 3,500 ac-ft
- Max storage
- 4,800 ac-ft
- Drainage area
- 134 sq mi
- Hazard class
- High
- Owner
- City Of Amery
Source: USACE National Inventory of Dams, NID ID WI00172 · Operator website · Matched by proximity (0.85 km)
Graded lakes near South Twin Lake
South Twin Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Polk County
Frequently asked questions about South Twin Lake
What is the water quality grade for South Twin Lake?
- South Twin Lake in Polk County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 11.7 µg/L. Maximum depth: 9 ft. Surface area: 72 acres.
Is South Twin Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. South Twin 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 Twin Lake?
- South Twin Lake has a maximum depth of 9 feet. The lake covers 72 acres.
What fish are in South Twin Lake?
- Fish species found in South Twin Lake include Panfish, Largemouth Bass, Northern Pike. South Twin Lake is located in Polk County, Wisconsin.
Are there boat ramps on South Twin Lake?
- South Twin Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include South Twin Lake. Public access is listed as yes.
Explore South Twin Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Where this data comes from
2 measurements from 1 monitoring station, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX2 samples · 2025
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
Named boat-access points from the USGS National Boat Ramps inventory