Big Thunder Lake
Beltrami County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for Big Thunder Lake. Here is what has been measured.
- Mesotrophic
Big Thunder Lake in Beltrami County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 11.5 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 3.7 µg/L.
Big Thunder Lake is a mesotrophic lake in Beltrami County, Minnesota. Water clarity is declining over recent sampling years. Compared to the 84 other monitored lakes in Beltrami County, Big Thunder Lake ranks #49 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-10. Methodology: how these readings are compared.
What Big Thunder Lake is good for
From access and monitoring records, not editorial picks.
- Clear water11.5 ft of visibility
Swimming conditions
Readings onlyLow algae
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 Big Thunder 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 Big Thunder Lake
These are the measurements Minnesota PCA publishes for Big Thunder 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 11.5 ft. Phosphorus 12 µg/L. Chlorophyll-a 3.7 µg/L. TSI 42.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 11.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 12µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3.7µg/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 Big Thunder Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Big Thunder Lake typically sits around 61°F at the surface in September. Summer average is about 73°F. Usually warmest in Jul (about 76°F) and coldest in Feb (about 34°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (34°F) to its warmest (76°F).
Typical surface water temperature by month, from 58 field readings (2010–2025) via the EPA Water Quality Portal. See the full Big Thunder Lake water temperature breakdown →
Stays via Stay22
Stays near Big Thunder Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Thunder Lake in Beltrami 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 Big Thunder Lake
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Fishing Big Thunder Lake
Water Quality Trend: Stable
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening6 years
Phosphorus
Improving-0.33 µg/L/yr6 years
Chlorophyll-a
Stable+0.03 µg/L/yr6 years
Nearby Lakes in Beltrami County
Frequently asked questions about Big Thunder Lake
Where is Big Thunder Lake?
- Big Thunder Lake is a lake in Beltrami County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Big Thunder Lake?
- Big Thunder Lake in Beltrami County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 11.5 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 3.7 µg/L.
Is Big Thunder Lake 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 Big Thunder Lake?
- Big Thunder Lake typically sits around 61°F at the surface in September, from 58 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
Explore Big Thunder Lake across LakeQuality
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Where this data comes from
87 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Red Lake DNR
REDLAKE_WQX87 samples · 2020–2025
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
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.