Bighorn Lake
Big Horn County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Bighorn Lake. Here is what has been measured.
- Eutrophic
- Limited data
Bighorn Lake in Big Horn County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 37 µg/L. Chlorophyll-a (algae): 17.1 µg/L.
Bighorn Lake is a productive, nutrient-rich eutrophic lake in Big Horn County, Montana. Compared to the 3 other monitored lakes in Big Horn County, Bighorn Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2019-08-14. 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 Bighorn Lake is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Bighorn Lake
These are the measurements Montana DEQ publishes for Bighorn Lake, 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 37 µg/L. Chlorophyll-a 17.1 µg/L. TSI 57.
| 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 | 37µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 17.1µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 57 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
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Nearby Lakes in Big Horn County
Frequently asked questions about Bighorn Lake
Where is Bighorn Lake?
- Bighorn Lake is a lake in Big Horn County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Bighorn Lake?
- Bighorn Lake in Big Horn County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 37 µg/L. Chlorophyll-a (algae): 17.1 µg/L.
Is Bighorn Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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Where this data comes from
37 measurements from 16 monitoring stations, 2015–2019. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Montana Water Science Center
USGS-MT37 samples · 2015–2019
Analytical methods
- P, wu, WCA, persulfate CF color
- Plant pigments, sonication & 445
Monitoring station identifiers (16)
- USGS-450104108151501
- USGS-450248108140501
- USGS-450311108133601
- USGS-450112108135801
- USGS-450416108140101
- USGS-450629108111401
- USGS-450538108125501
- USGS-450903108101001
- USGS-451310108062301
- USGS-451007108090601
- USGS-451248108074201
- USGS-451536108012801
- USGS-451640108001801
- USGS-451407108044001
- USGS-451519108035001
- USGS-451803107575201
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.