South Twin Lake
South Twin Lake in Mahnomen County, Minnesota has a water quality grade of A (Excellent). 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.
- Clarity
- 10.2 ft
- Typical in August
- 73°F
- Max depth
- 29 ft
- Area
- 1,127 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 17
Next lake in Mahnomen County
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. Water quality is graded A based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyBacteria A
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.
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.
Water Quality Grade: A (Excellent)
Good clarity, visible to about 10.2 ft. Phosphorus level: 13.5 µg/L. Chlorophyll-a: 3.1 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.2 ft | Not graded |
| Phosphorus | 13.5 µg/L | Good |
| Chlorophyll-a (Algae) | 3.1 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay 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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Water Temperature
South Twin Lake typically sits around 73°F at the surface in August. 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.
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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 29 ft |
| Surface Area | 1,127 acres |
| Shoreline Length | 5.1 mi |
| Littoral Zone | 47% |
| 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.
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2024-08-13 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 26.62 | 0.14 lb |
| Largemouth Bass | 10.82 | 0.72 lb |
| Yellow Perch | 9.66 | 0.12 lb |
| Northern Pike | 6.70 | 1.63 lb |
| IOD | 5.04 | — |
| Walleye | 3.81 | 2.26 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
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
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +1.1 m/yr | 2 |
| Phosphorus | ↑ Improving | -2 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -4.6 µg/L/yr | 2 |
Ice Season
Historical ice data from Minnesota DNR (10 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-25 (2012) | 2013-05-12 (2013) |
Most recent ice-out: 2025-04-19
County Ranking
Ranked #3 of 12 lakes in Mahnomen County
Nearby Lakes in Mahnomen County
Frequently asked questions about South Twin Lake
What is the water quality grade for South Twin Lake?
- South Twin Lake in Mahnomen County, Minnesota has a water quality grade of A (Excellent). 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 works out to a bacteria swim-safety grade of A — a historical summary of past testing, not a current reading. South Twin Lake has a water quality grade of A (Excellent). Bacteria levels can spike quickly after heavy rain, so always check Minnesota's current beach and health-department advisories before you swim.
What is the water temperature of South Twin Lake?
- South Twin Lake typically sits around 73°F at the surface in August, 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.
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.
Explore South Twin Lake across LakeGrade
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Species activity outlook by water temperature and season
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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)
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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate