Grassy Lake Dam is an earth dam located in Teton County, Wyoming, built in 1939. It carries a High hazard potential classification.
Dam profile
NID height · 118 ft118 ft tall and 1,170 ft long, taller than 98% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Grassy Lake Dam
The primary purpose of Grassy Lake Dam is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Bureau of Reclamation (federal). It impounds the Grassy Creek near St Anthony, Id.
The dam stands 118 feet tall and stretches 1,170 feet across, creates a reservoir covering 318 acres, has a maximum storage capacity of 16,210 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1939, the structure is well-established, with more than 75 years of service.
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. An emergency action plan is in place for this dam. The most recent inspection on record was 07/29/2020.
At 118 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 | Teton |
| Nearest City | St Anthony, Id |
| River/Stream | Grassy Creek |
| Coordinates | 44.13040, -110.81850 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 118 ft |
| Dam Height | 118 ft |
| Dam Length | 1,170 ft |
| Year Completed | 1939 (87 years old) |
Storage & Hydraulics
| NID Storage | 16,210 acre-ft |
| Max Storage | 16,210 acre-ft |
| Normal Storage | 15,470 acre-ft |
| Surface Area | 318 acres |
| Drainage Area | 3 sq mi |
| Max Discharge | 1,651 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | Bureau of Reclamation |
| Owner Type | Federal |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 07/29/2020 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WY01384 |
| Federal ID | WY01384 |
| More Info | State Dam Safety Program |