South Turtle Lake
South Turtle Lake in Otter Tail County, Minnesota has a water quality grade of A (Excellent). Water clarity: 14.1 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 3.7 µg/L. Maximum depth: 35 ft. Surface area: 836.57 acres.
- Clarity
- 14.1 ft
- Typical in August
- 74°F
- Max depth
- 35 ft
- Area
- 837 acres
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 20
- Open water
- 220 days
Next lake in Otter Tail County
Free interactive depth-contour map of South Turtle Lake, reaching a maximum surveyed depth of 30 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
South Turtle Lake is a 837-acre mesotrophic lake in Otter Tail County, Minnesota with a maximum depth of 35 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 13 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 65 other monitored lakes in Otter Tail County, South Turtle Lake ranks #33 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 14.1 ft. Phosphorus level: 20 µg/L. Chlorophyll-a: 3.7 µg/L. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 14.1 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | 3.7 µg/L | Good |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near South Turtle Lake
Compare lakeside cabins, hotels, and vacation rentals near South Turtle Lake in Otter Tail 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 Turtle Lake typically sits around 74°F at the surface in August. Summer average is about 73°F. Usually warmest in Jul (about 77°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 33 field readings (2010–2025) via the EPA Water Quality Portal. See the full South Turtle Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 35 ft |
| Surface Area | 837 acres |
| Shoreline Length | 11 mi |
| Littoral Zone | 48% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- South Turtle LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing South Turtle Lake
DNR Fisheries Survey Summary
7 surveys on file from MN DNR Fisheries. Most recent: 2018-07-24 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 37.96 | 0.16 lb |
| Yellow Bass | 16.56 | 0.5 lb |
| Bluntnose Minnow | 12.53 | — |
| BCS | 12.17 | — |
| Green Sunfish | 12.13 | 0.01 lb |
| Black Bullhead | 8.92 | 0.44 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
Yellow Bass
Green Sunfish
Black Bullhead
From the 2018-07-24 survey
A targeted survey of the nearshore fish community in South Turtle Lake was conducted by Fisheries Index of Biological Integrity (IBI) Program Staff starting July 24, 2018 on South Turtle Lake. Fourteen sampling sites were evenly spaced around the lake and each was sampled by backpack electrofishing and seining with a…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for South Turtle 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 TurtleFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — South Turtle (1189)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — South TurtleFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — South TurtlePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.041 m/yr | 6 |
| Phosphorus | → Stable | -0.2 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.13 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (16 observations).
Estimated open water season: 220 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-05 (2024) | 2013-05-11 (2013) |
| Ice-In | 2018-11-13 (2018) | 2017-12-12 (2017) |
Most recent ice-out: 2024-03-05
EPA Impairment Status
South Turtle Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN56-0377-00 · Official waterbody report
County Ranking
Ranked #33 of 66 lakes in Otter Tail County
Nearby Lakes in Otter Tail County
Frequently asked questions about South Turtle Lake
What is the water quality grade for South Turtle Lake?
- South Turtle Lake in Otter Tail County, Minnesota has a water quality grade of A (Excellent). Water clarity: 14.1 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 3.7 µg/L. Maximum depth: 35 ft. Surface area: 836.57 acres.
Is South Turtle Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. South Turtle Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 3.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of South Turtle Lake?
- South Turtle Lake typically sits around 74°F at the surface in August, from 33 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is South Turtle Lake?
- South Turtle Lake has a maximum depth of 35 feet. The lake covers 836.57 acres.
What fish are in South Turtle Lake?
- Fish species found in South Turtle Lake include black bullhead, black crappie, bluegill, brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. South Turtle Lake is located in Otter Tail County, Minnesota.
When does South Turtle Lake thaw?
- South Turtle Lake typically has ice-out around Apr 20. Ice typically forms around Nov 26. The open water season is approximately 220 days.
Are there boat ramps on South Turtle Lake?
- South Turtle Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include South Turtle Lake. Public access is listed as yes.
Explore South Turtle Lake across LakeGrade
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Where this data comes from
188 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA188 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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
Impairment status from EPA ATTAINS 303(d) database
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