Guernsey Reservoir
Platte County, Wyoming2,380 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Eutrophic
- #5 of 9 in the county
- Limited data
Guernsey Reservoir in Platte County, Wyoming has a water quality grade of B (Good). Water clarity: 4.9 ft visibility. Phosphorus: 20 µg/L. Surface area: 2380 acres.
- Clarity
- 4.9 ft
- Area
- 2,380 acres
- Type
- Eutrophic
- Phosphorus
- 20 µg/L
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Watch Guernsey Reservoir’s letter
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Guernsey Reservoir is a 2,380-acre productive, nutrient-rich eutrophic lake in Platte County, Wyoming. Water quality is graded B based on 1 sampling years through 2018. Compared to the 8 other monitored lakes in Platte County, Guernsey Reservoir ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Wyoming DEQ, last sampled 2018-09-05. Grade methodology: LakeQuality methodology.
What Guernsey Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water2,380 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)
Murky, only visible to about 4.9 ft. Phosphorus 20 µg/L. TSI 51. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.9 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 2,380 acres |
No bathymetric survey has been published for Guernsey Reservoir, so its depth is not documented here.
Fishing Guernsey Reservoir
Reservoir Info (USACE NID)
Guernsey Reservoir is a man-made reservoir impounded by the Guernsey Dam (completed 1927), built primarily for hydroelectric on the North Platte River; earth-type dam, 137 ft tall and 560 ft long.
- Surface area
- 2,380 ac
- Normal storage
- 45,612 ac-ft
- Max storage
- 45,612 ac-ft
- Drainage area
- 15,847.9 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Hydroelectric;Irrigation.
Source: USACE National Inventory of Dams, NID ID WY01293 · Operator website
County Ranking
Ranked #5 of 9 lakes in Platte County
Nearby Lakes in Platte County
Frequently asked questions about Guernsey Reservoir
Where is Guernsey Reservoir?
- Guernsey Reservoir is a lake in Platte County, Wyoming. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Guernsey Reservoir?
- Guernsey Reservoir in Platte County, Wyoming has a water quality grade of B (Good). Water clarity: 4.9 ft visibility. Phosphorus: 20 µg/L. Surface area: 2380 acres.
Is Guernsey Reservoir safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Guernsey Reservoir across LakeQuality
4.5 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
Wyoming's cleanest and most-polluted lakes, ranked
More Wyoming Lake Rankings
Other Grade B Lakes in Wyoming
Eutrophic Lakes in Wyoming
Where this data comes from
12 measurements from 3 monitoring stations, 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_WATERSHED12 samples · 2018
Analytical methods
- Secchi
- Total Phosphorus After Block Digestion
Monitoring station identifiers (3)
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.