Guernsey Reservoir
Platte County, Wyoming2,380 acresView mapDirections
Wyoming DEQ publishes the water-quality measurements for Guernsey Reservoir. Here is what has been measured.
- Eutrophic
- Limited data
Guernsey Reservoir in Platte County, Wyoming has water-quality measurements published by Wyoming DEQ, shown here as reported. Water clarity: 4.9 ft visibility. Phosphorus: 20 µg/L. Surface area: 2380 acres.
Guernsey Reservoir is a 2,380-acre productive, nutrient-rich eutrophic lake in Platte County, Wyoming. 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. Methodology: how these readings are compared.
Guernsey Reservoir covers about 2,400 acres in Platte County. Vrbo is where to look for cabins and lake homes around Guernsey Reservoir, and Booking.com and Expedia search hotels near the lake for your dates.
What Guernsey Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water2,380 acres
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Guernsey Reservoir is safe to swim in today is a call for the Wyoming Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Guernsey Reservoir
These are the measurements Wyoming DEQ publishes for Guernsey Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 4.9 ft. Phosphorus 20 µg/L. TSI 51.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 20µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 51 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Guernsey Reservoir
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Lake Details
Surface area
2,380 acres
No bathymetric survey has been published for Guernsey Reservoir, so its depth is not documented here.
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Stays near Guernsey Reservoir
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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
Nearby Lakes in Platte County
Frequently asked questions about Guernsey Reservoir
Where is Guernsey Reservoir?
- Guernsey Reservoir is a lake in Platte County, Wyoming. Its water-quality measurements are published by Wyoming DEQ and shown on this page as reported.
What is the water quality of Guernsey Reservoir?
- Guernsey Reservoir in Platte County, Wyoming has water-quality measurements published by Wyoming DEQ, shown here as reported. Water clarity: 4.9 ft visibility. Phosphorus: 20 µg/L. Surface area: 2380 acres.
Is Guernsey Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Guernsey Reservoir across LakeQuality
4.5 mi away · recorded at 70°F
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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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.