Unnamed Reservoir
Big Horn County, Wyoming34 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from F at the last regrade
- Eutrophic
- #3 of 5 in the county
- Limited data
Unnamed Reservoir in Big Horn County, Wyoming has a water quality grade of C (Fair). Phosphorus: 65 µg/L. Surface area: 34 acres.
- Area
- 34 acres
- Type
- Eutrophic
- Phosphorus
- 65 µg/L
- Trend
- ↓ Declining
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Watch Unnamed Reservoir’s letter
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Unnamed Reservoir is a 34-acre productive, nutrient-rich eutrophic lake in Big Horn County, Wyoming. Water quality is graded C based on 1 sampling years through 2016. Overall water quality is declining over recent sampling years. Compared to the 4 other monitored lakes in Big Horn County, Unnamed Reservoir ranks #3 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 C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 65 µg/L. TSI 64. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 65 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 34 acres |
No bathymetric survey has been published for Unnamed Reservoir, so its depth is not documented here.
Fishing Unnamed Reservoir
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +5 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Unnamed Reservoir is a man-made reservoir impounded by the Bench Canal (completed 1969), built primarily for irrigation on the Greybull River; earth-type dam, 35 ft tall and 1,000 ft long.
- Surface area
- 34 ac
- Normal storage
- 299 ac-ft
- Max storage
- 497 ac-ft
- Drainage area
- 1 sq mi
- Hazard class
- Low
- Owner
- BENCH CANAL COMPANY
Source: USACE National Inventory of Dams, NID ID WY01086 · Operator website · Matched by proximity (0.27 km)
County Ranking
Ranked #3 of 5 lakes in Big Horn County
Nearby Lakes in Big Horn County
Frequently asked questions about Unnamed Reservoir
Where is Unnamed Reservoir?
- Unnamed Reservoir is a lake in Big Horn County, Wyoming. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Unnamed Reservoir?
- Unnamed Reservoir in Big Horn County, Wyoming has a water quality grade of C (Fair). Phosphorus: 65 µg/L. Surface area: 34 acres.
Is Unnamed Reservoir safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Unnamed Reservoir across LakeQuality
12.5 mi away · recorded at 70°F
Species activity outlook by water temperature and season
Where to stay at Wyoming's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
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Other Grade C Lakes in Wyoming
Eutrophic Lakes in Wyoming
Where this data comes from
12 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_WATERSHED12 samples · 2015–2016
Analytical methods
- 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.