Bighorn Lake
Big Horn County, MontanaView mapDirections
Nutrients and algae sit mid-range for this region.
- Eutrophic
- #4 of 4 in the county
- Limited data
Bighorn Lake in Big Horn County, Montana has a water quality grade of C (Fair). Phosphorus: 37 µg/L. Chlorophyll-a (algae): 17.1 µg/L.
- Type
- Eutrophic
- Phosphorus
- 37 µg/L
- Chlorophyll-a
- 17.1 µg/L
Stays via Stay22
Stays near Bighorn Lake
Compare lakeside cabins, hotels, and vacation rentals near Bighorn Lake in Big Horn County, Montana — 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 Bighorn Lake
Prices for Sep 11–13, 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 Montana’s top lakes →
Watch Bighorn Lake’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
Bighorn Lake is a productive, nutrient-rich eutrophic lake in Big Horn County, Montana. Water quality is graded C based on 2 sampling years through 2019. 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. Grade methodology: LakeQuality methodology.
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.
The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 37 µg/L. Chlorophyll-a 17.1 µg/L. TSI 57. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 37 µg/L | Good |
| Chlorophyll-a (Algae) | 17.1 µg/L | Fair |
| Trophic State Index (TSI) | 57 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Fishing Bighorn Lake
County Ranking
Ranked #4 of 4 lakes in Big Horn County
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. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Bighorn Lake?
- Bighorn Lake in Big Horn County, Montana has a water quality grade of C (Fair). Phosphorus: 37 µg/L. Chlorophyll-a (algae): 17.1 µg/L.
Is Bighorn Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Bighorn Lake across LakeQuality
More Montana Lake Rankings
Other Grade C Lakes in Montana
Eutrophic Lakes in Montana
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
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.