Turtle Lake Deep
Turtle Lake Deep in Cook County, Minnesota has a water quality grade of A (Excellent). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2 µg/L.
- Typical in August
- 75°F
- Type
- Mesotrophic
- Trend
- → Stable
Next lake in Cook County
Turtle Lake Deep is a mesotrophic lake in Cook County, Minnesota. Water quality is graded A based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
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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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
No clarity data. Phosphorus level: 22 µg/L. Chlorophyll-a: 2 µg/L. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 22 µg/L | Good |
| Chlorophyll-a (Algae) | 2 µg/L | Good |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay 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.
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Water Temperature
Turtle Lake Deep typically sits around 75°F at the surface in August. 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.
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 →
Fishing Turtle Lake Deep
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -10.222 m/yr | 4 |
| Phosphorus | ↑ Improving | -2.49 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | -0.03 µg/L/yr | 4 |
County Ranking
Ranked #24 of 44 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Turtle Lake Deep
What is the water quality grade for Turtle Lake Deep?
- Turtle Lake Deep in Cook County, Minnesota has a water quality grade of A (Excellent). Phosphorus: 22 µg/L. Chlorophyll-a (algae): 2 µg/L.
Is Turtle Lake Deep safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Turtle Lake Deep has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Turtle Lake Deep?
- Turtle Lake Deep typically sits around 75°F at the surface in August, 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 LakeGrade
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Moderate nutrients, good water quality
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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)
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.