Keyhole Reservoir
Crook County, Wyoming9,411 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
- Mesotrophic
- #1 of 3 in the county
- Public access
- Limited data
Keyhole Reservoir in Crook County, Wyoming has a water quality grade of B (Good). Water clarity: 7.7 ft visibility. Phosphorus: 20 µg/L. Surface area: 9411 acres.
- Clarity
- 7.7 ft
- Area
- 9,411 acres
- Type
- Mesotrophic
- Phosphorus
- 20 µg/L
- Trend
- → Stable
- Public access
- Yes
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Watch Keyhole Reservoir’s letter
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Keyhole Reservoir is a 9,411-acre mesotrophic lake in Crook County, Wyoming. Water quality is graded B based on 1 sampling years through 2018. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 2 other monitored lakes in Crook County, Keyhole Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wyoming DEQ, last sampled 2018-09-10. Grade methodology: LakeQuality methodology.
What Keyhole Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
- Big water9,411 acres
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 B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: B (Good)
Moderate clarity, visible to about 7.7 ft. Phosphorus 20 µg/L. TSI 48. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.7 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 9,411 acres |
| Public Access | Yes |
No bathymetric survey has been published for Keyhole Reservoir, so its depth is not documented here.
Recreation & Access
- Keyhole State PArkPublic
- Keyhole MarinaSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Keyhole Reservoir
Water Quality Trend: → Stable
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | → Stable | 0 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Keyhole Reservoir is a man-made reservoir impounded by the Keyhole Dam (completed 1952), built primarily for flood risk reduction on the Belle Fourche River; earth-type dam, 168 ft tall and 3,420 ft long.
- Surface area
- 9,411 ac
- Normal storage
- 334,215 ac-ft
- Max storage
- 629,025 ac-ft
- Drainage area
- 1,949.73 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Flood Risk Reduction;Irrigation.
Source: USACE National Inventory of Dams, NID ID WY01380 · Operator website
County Ranking
Ranked #1 of 3 lakes in Crook County
Nearby Lakes in Crook County
Frequently asked questions about Keyhole Reservoir
Where is Keyhole Reservoir?
- Keyhole Reservoir is a lake in Crook County, Wyoming. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Keyhole Reservoir?
- Keyhole Reservoir in Crook County, Wyoming has a water quality grade of B (Good). Water clarity: 7.7 ft visibility. Phosphorus: 20 µg/L. Surface area: 9411 acres.
Is Keyhole Reservoir safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Are there boat ramps on Keyhole Reservoir?
- Keyhole Reservoir has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Keyhole State PArk, Keyhole Marina. Public access is listed as yes.
Explore Keyhole Reservoir across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Wyoming's top lakes, each with its grade
Moderate nutrients, good water quality
Wyoming's cleanest and most-polluted lakes, ranked
Planning a trip around Devils Tower?
Keyhole Reservoir is about 15 miles from Devils Tower National Monument. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Devils Tower →More Wyoming Lake Rankings
Other Grade B Lakes in Wyoming
Mesotrophic Lakes in Wyoming
Where this data comes from
9 measurements from 1 monitoring station, 2017–2018. 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_WATERSHED9 samples · 2017–2018
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.
Other records on this page
Named boat-access points from the USGS National Boat Ramps inventory