Lake Desmet (a,b,c & Spillway Dikes)
Lake Desmet (a,b,c & Spillway Dikes) is an earth dam located in Johnson County, Wyoming, built in 1975. It carries a High hazard potential classification and has a fair condition assessment.
About Lake Desmet (a,b,c & Spillway Dikes)
The primary purpose of Lake Desmet (a,b,c & Spillway Dikes) is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by Johnson County-lake Desmet Operating Dept (local government). It impounds the Piney And Rock Creek near Ucross.
The dam stands 120 feet tall and stretches 4,000 feet across, creates a reservoir covering 2,653 acres, has a maximum storage capacity of 234,987 acre-feet, and collects water from a drainage area of 40 square miles. Completed in 1975, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 06/26/2024.
At 120 feet, this dam is taller than 98% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Wyoming dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Wyoming |
| County | Johnson |
| Nearest City | Ucross |
| River/Stream | Piney And Rock Creek |
| Coordinates | 44.48900, -106.74400 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 120 ft |
| Dam Height | 80 ft |
| Dam Length | 4,000 ft |
| Year Completed | 1975 (51 years old) |
Storage & Hydraulics
| NID Storage | 234,987 acre-ft |
| Max Storage | 234,987 acre-ft |
| Normal Storage | 111,827 acre-ft |
| Surface Area | 2,653 acres |
| Drainage Area | 40 sq mi |
| Max Discharge | 8,520 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | JOHNSON COUNTY-LAKE DESMET OPERATING DEPT |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 06/26/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WY02303 |
| Federal ID | WY02303 |
| More Info | State Dam Safety Program |