Guernsey Reservoir Report
Nearby: Whalen Diversion Dam Grayrocks
Last Updated: December 5, 2025
Guernsey, located in Platte, Wyoming, is a federal-owned dam along the North Platte River with a primary purpose of hydroelectric power generation and irrigation.
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Summary
Built in 1926, this earth dam stands at 135 feet high and has a storage capacity of 45,612 acre-feet. With a surface area of 2,380 acres and a drainage area of 15,008 square miles, Guernsey plays a crucial role in water resource management in the region.
Managed by the Bureau of Reclamation, Guernsey has undergone structural modifications in 1984 and 2016 to ensure its safety and functionality. The dam is equipped with a controlled spillway and tainter gates for water release, with a high hazard potential due to its location and design. Despite its age, the condition assessment of Guernsey is currently not available, highlighting the need for ongoing monitoring and maintenance to safeguard against potential risks and ensure its continued operation for both hydroelectric power generation and irrigation purposes.
With Liz Cheney (R) as the congressional representative for the area, Guernsey remains a vital component of the water infrastructure in Wyoming. As a key player in regulating and inspecting the dam, the Bureau of Reclamation is responsible for its operations and ensuring compliance with state regulatory agencies. Water resource and climate enthusiasts can appreciate the engineering feats and environmental impact of Guernsey, a historic structure that continues to serve the community while facing challenges of aging infrastructure and evolving safety standards in the face of climate change.
Years Modified |
1984 - Structural, 2016 - Structural |
Year Completed |
1926 |
Dam Length |
560 |
Dam Height |
135 |
River Or Stream |
NORTH PLATTE RIVER |
Primary Dam Type |
Earth |
Surface Area |
2380 |
Hydraulic Height |
92 |
Drainage Area |
15008 |
Nid Storage |
45612 |
Structural Height |
135 |
Outlet Gates |
Tainter (radial) |
Hazard Potential |
High |
Foundations |
Soil |
Nid Height |
135 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Area Campgrounds
| Location | Reservations | Toilets |
|---|---|---|
Guernsey State Park
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Larson Park
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Grayrocks Reservoir Public Access - WGF
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Guernsey