Lake Desmet (A Reservoir Report

Last Updated: December 5, 2025

Lake Desmet (A,B,C & Spillway Dikes) is a significant water resource located in the beautiful state of Wyoming.


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Summary

Constructed in 1975, this earth dam stands at a height of 80 feet, with a structural height of 120 feet and a hydraulic height of 70 feet. With a maximum storage capacity of 234,987 acre-feet and a normal storage capacity of 111,827 acre-feet, Lake Desmet plays a crucial role in providing water supply to the surrounding areas.

Situated in Johnson County, Wyoming, Lake Desmet spans across 2,653 acres with a drainage area of 40.5 square miles. The dam is primarily used for water supply purposes and is regulated by the State of Wyoming, with inspections conducted regularly to ensure its safety and integrity. The spillway, with a width of 200 feet, is designed to handle a maximum discharge of 8,520 cubic feet per second, making it a crucial component in managing water levels during periods of high flow.

Despite being classified as having a high hazard potential, Lake Desmet's condition assessment is rated as fair, with the last inspection conducted in July 2019. With its strategic location and vital role in water management, Lake Desmet (A,B,C & Spillway Dikes) serves as a key infrastructure for water resource and climate enthusiasts to study and appreciate the intricate balance between human development and natural ecosystems in the region.

Year Completed

1975

Dam Length

4000

Dam Height

80

River Or Stream

PINEY AND ROCK CREEK

Primary Dam Type

Earth

Surface Area

2653

Hydraulic Height

70

Drainage Area

40.5

Nid Storage

234987

Structural Height

120

Outlet Gates

Valve - 1

Hazard Potential

High

Foundations

Soil

Nid Height

120
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.