Horseshoe Reservoir
Big Horn County, Wyoming28 acresView mapDirections
Nutrients and algae run above the regional average.
↑ up from F at the last regrade
- Hypereutrophic
- #4 of 5 in the county
- Limited data
Horseshoe Reservoir in Big Horn County, Wyoming has a water quality grade of D (Nutrient-rich). Water clarity: 1.8 ft visibility. Phosphorus: 140 µg/L. Surface area: 28 acres.
- Clarity
- 1.8 ft
- Area
- 28 acres
- Type
- Hypereutrophic
- Phosphorus
- 140 µg/L
- Trend
- ↑ Improving
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Compare lakeside cabins, hotels, and vacation rentals near Horseshoe Reservoir in Big Horn County, Wyoming — 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Horseshoe Reservoir are listed below.
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Watch Horseshoe Reservoir’s letter
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Horseshoe Reservoir is a 28-acre highly nutrient-loaded hypereutrophic lake in Big Horn County, Wyoming. Water quality is graded D based on 1 sampling years through 2016. Overall water quality is improving over recent sampling years. Compared to the 4 other monitored lakes in Big Horn County, Horseshoe Reservoir ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Wyoming DEQ, last sampled 2016-09-20. 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 D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 1.8 ft of visibility. Phosphorus 140 µg/L. TSI 72. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.8 ft | Not graded |
| Phosphorus | 140 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 28 acres |
No bathymetric survey has been published for Horseshoe Reservoir, so its depth is not documented here.
Fishing Horseshoe Reservoir
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↑ Improving | -60 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Horseshoe Reservoir is a man-made reservoir impounded by the Horseshoe (completed 1969), built primarily for fish and wildlife pond on the Trail Draw; earth-type dam, 30 ft tall and 268 ft long.
- Surface area
- 28 ac
- Normal storage
- 145 ac-ft
- Max storage
- 329 ac-ft
- Drainage area
- 0 sq mi
- Hazard class
- Low
- Owner
- WYOMING GAME AND FISH COMMISSION
Source: USACE National Inventory of Dams, NID ID WY01123 · Operator website
County Ranking
Ranked #4 of 5 lakes in Big Horn County
Nearby Lakes in Big Horn County
Frequently asked questions about Horseshoe Reservoir
Where is Horseshoe Reservoir?
- Horseshoe Reservoir is a lake in Big Horn County, Wyoming. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Horseshoe Reservoir?
- Horseshoe Reservoir in Big Horn County, Wyoming has a water quality grade of D (Nutrient-rich). Water clarity: 1.8 ft visibility. Phosphorus: 140 µg/L. Surface area: 28 acres.
Is Horseshoe Reservoir safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Horseshoe Reservoir across LakeQuality
16.4 mi away · 200 ft
2 thermal springs within 19.7 mi, nearest Little Sheep Mountain Spring
Species activity outlook by water temperature and season
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Very high nutrients, dense algae, poor clarity
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Where this data comes from
7 measurements from 1 monitoring station, 2015–2016. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- State of Wyoming Department of Environmental Quality Watershed Program
WYDEQ_WATERSHED7 samples · 2015–2016
Analytical methods
- Secchi
- Total Phosphorus After Block Digestion
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.