South Twin Lake
Mahnomen County, Minnesota1,127 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for South Twin Lake. Here is what has been measured.
- Mesotrophic
- zebra mussel
- 29 ft max depth
- Public access
South Twin Lake in Mahnomen County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 10.2 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 3.1 µg/L. Maximum depth: 29 ft. Surface area: 1127 acres.
Minnesota DNR's Targeted Survey on August 13, 2024 caught 8.39 largemouth bass per hour of electrofishing at South Twin Lake. Length samples in the latest survey that recorded them ran 5–18 inches. DNR survey details →
Free interactive depth-contour map of South Twin Lake, reaching a maximum surveyed depth of 25 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
South Twin Lake is a 1,127-acre mesotrophic lake in Mahnomen County, Minnesota with a maximum depth of 29 feet. Overall water quality is improving over recent sampling years. The lake supports 15 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 11 other monitored lakes in Mahnomen County, South Twin Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-06. Methodology: how these readings are compared.
What South Twin Lake is good for
From access and monitoring records, not editorial picks.
- Clear water10.2 ft of visibility
- Boat launch1 documented ramp
- Fishing15 species recorded
- Ice seasonIce-out around Apr 17
- Big water1,127 acres
Swimming conditions
Readings onlyBacteria tested: low
Based on clarity and algae readings from past sampling — there is no 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, South Twin Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 6 samples across 2 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Minnesota’s current beach and health-department advisories before swimming.
Whether South Twin Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for South Twin Lake
These are the measurements Minnesota PCA publishes for South Twin Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 10.2 ft. Phosphorus 13.5 µg/L. Chlorophyll-a 3.1 µg/L. TSI 42.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 10.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 13.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3.1µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 42 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about South Twin Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
South Twin Lake typically sits around 57°F at the surface in October. Summer average is about 71°F. Usually warmest in Jul (about 74°F) and coldest in May (about 53°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (53°F) to its warmest (74°F).
Typical surface water temperature by month, from 177 field readings (2010–2025) via the EPA Water Quality Portal. See the full South Twin Lake water temperature breakdown →
Minnesota DNR's Targeted Survey on August 13, 2024 caught 8.39 largemouth bass per hour of electrofishing at South Twin Lake. Length samples in the latest survey that recorded them ran 5–18 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows South Twin Lake’s water-quality measurements separately, and the water-quality trend over 2 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2024-08-13 (Targeted Survey).
12 surveys on file · most recent 2024-08-13 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 26.62 | 2–9 in 2024-07-08 | 0.14 lb |
| Largemouth Bass | 10.82 | 5–18 in 2024-07-08 | 0.72 lb |
| Yellow Perch | 9.66 | 5–10 in 2024-07-08 | 0.12 lb |
| Northern Pike | 6.70 | 11–34 in 2024-07-08 | 1.63 lb |
| Walleye | 3.81 | 9–25 in 2024-07-08 | 2.26 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Bluegill
Largemouth Bass
Yellow Perch
Northern Pike
From the 2024-08-13 survey
A targeted survey of nearshore fish species in South Twin Lake was conducted on August 13th, and 14th, 2024, by Detroit Lakes Fisheries Staff. The survey consisted of 14 sampling stations evenly spaced around the lake. All stations were sampled with a backpack electrofishing unit, 11 were sampled with a 50-foot seine…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for South Twin Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — South TwinFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — South Twin (1946)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — South TwinFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — South TwinPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
29 ft
Surface area
1,127 acres
Shoreline
5.1 mi
Littoral zone
47%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
19 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,437 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- South Twin LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near South Twin Lake
Compare lakeside cabins, hotels, and vacation rentals near South Twin Lake in Mahnomen 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.
Top-rated places to stay near South Twin Lake
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Fish Species
Click a species to see every 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 readings over time
2 seasons of samples on record (2024–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
Phosphorus
Improving-2 µg/L/yr2 years
Chlorophyll-a
Improving-4.6 µg/L/yr2 years
Ice season
Typical ice-out
Apr 17
Earliest Mar 25, 2012 · Latest May 12, 2013
Most recent ice-out
Apr 19
2025
10 observations · Minnesota PCA ice records
Nearby Lakes in Mahnomen County
Frequently asked questions about South Twin Lake
Where is South Twin Lake?
- South Twin Lake is a lake in Mahnomen County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of South Twin Lake?
- South Twin Lake in Mahnomen County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 10.2 ft visibility. Phosphorus: 13.5 µg/L. Chlorophyll-a (algae): 3.1 µg/L. Maximum depth: 29 ft. Surface area: 1127 acres.
Is South Twin Lake safe to swim in?
- Based on E. coli testing, South Twin Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 6 samples across 2 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether South Twin Lake is safe to swim in today is a call for Minnesota's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of South Twin Lake?
- South Twin Lake typically sits around 57°F at the surface in October, from 177 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is South Twin Lake?
- South Twin Lake has a maximum depth of 29 feet. The lake covers 1127 acres.
What fish are in South Twin Lake?
- Fish species found in South Twin Lake include black bullhead, black crappie, bluegill, brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. South Twin Lake is located in Mahnomen County, Minnesota.
What did the DNR fisheries survey find at South Twin Lake?
- Minnesota DNR's Targeted Survey on August 13, 2024 caught 8.39 largemouth bass per hour of electrofishing at South Twin Lake. Length samples in the latest survey that recorded them ran 5–18 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows South Twin Lake’s water-quality measurements separately, and the water-quality trend over 2 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
When does South Twin Lake thaw?
- South Twin Lake typically has ice-out around Apr 17.
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.
Can I fish at South Twin Lake?
- South Twin Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
Explore South Twin Lake across LakeQuality
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Minnesota's cleanest lakes, ranked on agency measurements
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Compare South Twin Lake With Nearby Lakes
Where this data comes from
56 measurements from 3 monitoring stations, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Chippewa Tribe, Minnesota (White Earth Band) (Tribal)
WEARTH_WQX34 samples · 2024 - Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA22 samples · 2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
- Phosphorus by Colorimetry
Monitoring station identifiers (3)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate