Turtle Lake Deep
Cook County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for Turtle Lake Deep. Here is what has been measured.
- Mesotrophic
- Limited data
Turtle Lake Deep in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2 µg/L.
Turtle Lake Deep is a mesotrophic lake in Cook County, Minnesota. Water clarity is declining over recent sampling years. Compared to the 43 other monitored lakes in Cook County, Turtle Lake Deep ranks #24 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLimited data
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.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Turtle Lake Deep 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 Turtle Lake Deep
These are the measurements Minnesota PCA publishes for Turtle Lake Deep, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 22 µg/L. Chlorophyll-a 2 µg/L. TSI 43.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 22µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2µg/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. | 43 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Turtle Lake Deep
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Turtle Lake Deep typically sits around 57°F at the surface in October. Summer average is about 73°F. Usually warmest in Aug (about 75°F) and coldest in May (about 51°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (51°F) to its warmest (75°F).
Typical surface water temperature by month, from 107 field readings (2011–2025) via the EPA Water Quality Portal. See the full Turtle Lake Deep water temperature breakdown →
Stays via Stay22
Stays near Turtle Lake Deep
Compare lakeside cabins, hotels, and vacation rentals near Turtle Lake Deep in Cook 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 Turtle Lake Deep
Prices for Oct 9–11, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Follow Turtle Lake Deep’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Turtle Lake Deep
Water Quality Trend: Stable
Based on 5 years of monitoring (2020–2025).
Water clarity
Worsening4 years
Phosphorus
Improving-2.49 µg/L/yr4 years
Chlorophyll-a
Stable-0.03 µg/L/yr4 years
Nearby Lakes in Cook County
Frequently asked questions about Turtle Lake Deep
Where is Turtle Lake Deep?
- Turtle Lake Deep is a lake in Cook County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Turtle Lake Deep?
- Turtle Lake Deep in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2 µg/L.
Is Turtle Lake Deep safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Turtle Lake Deep?
- Turtle Lake Deep typically sits around 57°F at the surface in October, from 107 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
Explore Turtle Lake Deep across LakeQuality
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Cook County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
State Parks Near Turtle Lake Deep
Other Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Where this data comes from
24 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Grand Portage Reservation
GPC5_WQX24 samples · 2021–2025
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 5310 C ~ Total Organic Carbon in Water- Ultraviolet Oxidation Method
Monitoring station identifiers (1)
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.