St Marys River Watershed Site 1
St Marys River Watershed Site 1 is an earth dam located in St. Mary's County, Maryland, built in 1975. It carries a High hazard potential classification and has a fair condition assessment.
About St Marys River Watershed Site 1
The primary purpose of St Marys River Watershed Site 1 is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Md Dnr-public Lands, Engineering & Constr-southern (state). It impounds the Western Br, St. Marys River near Great Mills.
The dam stands 38 feet tall and stretches 1,670 feet across, creates a reservoir covering 250 acres, has a maximum storage capacity of 9,600 acre-feet, and collects water from a drainage area of 8 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 11/15/2024.
At 38 feet, this dam is taller than 85% of dams nationwide.
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 Maryland 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 | Maryland |
| County | St. Mary's |
| Nearest City | Great Mills |
| River/Stream | Western Br, St. Marys River |
| Coordinates | 38.25190, -76.53440 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 38 ft |
| Dam Height | 38 ft |
| Dam Length | 1,670 ft |
| Year Completed | 1975 (51 years old) |
Storage & Hydraulics
| NID Storage | 9,600 acre-ft |
| Max Storage | 9,600 acre-ft |
| Normal Storage | 3,200 acre-ft |
| Surface Area | 250 acres |
| Drainage Area | 8 sq mi |
| Max Discharge | 20,576 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | MD DNR-Public Lands, Engineering & Constr-Southern |
| Owner Type | State |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 11/15/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MD00028 |
| Federal ID | MD00028 |
| More Info | State Dam Safety Program |