Mountain Island
Mountain Island is a gravity dam located in Gaston County, North Carolina, built in 1923. It carries a High hazard potential classification and has a fair condition assessment.
About Mountain Island
The primary purpose of Mountain Island is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Duke Energy (public utility). It impounds the Catawba River near Mount Holly.
The dam stands 140 feet tall and stretches 2,375 feet across, creates a reservoir covering 3,235 acres, has a maximum storage capacity of 45,970 acre-feet, and collects water from a drainage area of 1,860 square miles. Completed in 1923, the structure is over a century 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 06/07/2022.
At 140 feet, this dam is taller than 99% 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 North Carolina 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 | North Carolina |
| County | Gaston |
| Nearest City | Mount Holly |
| River/Stream | Catawba River |
| Coordinates | 35.33580, -80.98484 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 140 ft |
| Dam Height | 140 ft |
| Dam Length | 2,375 ft |
| Year Completed | 1923 (103 years old) |
Storage & Hydraulics
| NID Storage | 45,970 acre-ft |
| Max Storage | 45,970 acre-ft |
| Normal Storage | 45,970 acre-ft |
| Surface Area | 3,235 acres |
| Drainage Area | 1,860 sq mi |
| Max Discharge | 383,685 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | Duke Energy |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 06/07/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NC00787 |
| Federal ID | NC00787 |
| More Info | State Dam Safety Program |