South Twin Lake
South Twin Lake in Washington County, Minnesota has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 32 µg/L. Chlorophyll-a (algae): 9 µg/L.
- Clarity
- 5 ft
- Typical in August
- 74°F
- Max depth
- ~37 ft est.
- Type
- Eutrophic
- Public access
- No
Next lake in Washington County
South Twin Lake is a productive, nutrient-rich eutrophic lake in Washington County, Minnesota with an estimated average depth of about 37 feet. Water quality is graded C based on 2 sampling years through 2024. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 74 other monitored lakes in Washington County, South Twin Lake ranks #32 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-17. Grade methodology: LakeGrade methodology.
Watch South Twin Lake water quality
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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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 5 ft. Phosphorus level: 32 µg/L. Chlorophyll-a: 9 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | Not graded |
| Phosphorus | 32 µg/L | Fair |
| Chlorophyll-a (Algae) | 9 µg/L | Fair |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near South Twin Lake
Compare lakeside cabins, hotels, and vacation rentals near South Twin Lake in Washington County, Minnesota — 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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Water Temperature
South Twin Lake typically sits around 74°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 77°F) and coldest in Apr (about 49°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 90 field readings (2010–2024) via the EPA Water Quality Portal. See the full South Twin Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~37 ft est. |
| Average Depth | ~7 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Minnesota has not published bathymetry for South Twin 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 South Twin Lake
County Ranking
Ranked #32 of 75 lakes in Washington County
Nearby Lakes in Washington County
Frequently asked questions about South Twin Lake
What is the water quality grade for South Twin Lake?
- South Twin Lake in Washington County, Minnesota has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 32 µg/L. Chlorophyll-a (algae): 9 µg/L.
Is South Twin Lake safe to swim in?
- Generally safe for swimming, moderate water quality. South Twin Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of South Twin Lake?
- South Twin Lake typically sits around 74°F at the surface in August, from 90 EPA Water Quality Portal field readings (2010–2024). That is a typical value for the month, not a live reading.
How deep is South Twin Lake?
- No published bathymetric survey covers South Twin Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 37 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore South Twin Lake across LakeGrade
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Where this data comes from
28 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA28 samples · 2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
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)
Lake details from Minnesota DNR LakeFinder