Rock Island Lake Dam is an earth dam located in Sussex County, New Jersey, built in 1940. It carries a Significant hazard potential classification and has a poor condition assessment.
Dam profile
NID height · 19 ft19 ft tall and 500 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Rock Island Lake Dam
The primary purpose of Rock Island Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Rock Island Lake Owners Assoc. (private). It impounds the Sparta Glen-tr near Sparta.
The dam stands 19 feet tall and stretches 500 feet across, creates a reservoir covering 11 acres, has a maximum storage capacity of 61 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1940, the structure is well-established, with more than 75 years of service.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. Its condition is rated poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 03/17/2024.
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Location
| State | New Jersey |
| County | Sussex |
| Nearest City | Sparta |
| River/Stream | Sparta Glen-tr |
| Coordinates | 41.04087, -74.58413 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 19 ft |
| Dam Height | 19 ft |
| Dam Length | 500 ft |
| Year Completed | 1940 (86 years old) |
Storage & Hydraulics
| NID Storage | 61 acre-ft |
| Max Storage | 61 acre-ft |
| Normal Storage | 50 acre-ft |
| Surface Area | 11 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 9 cfs |
Ownership & Safety
| Purpose | Recreation |
| Owner | Rock Island Lake Owners Assoc. |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Poor |
| Last Inspection | 03/17/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NJ00819 |
| Federal ID | NJ00819 |
| More Info | State Dam Safety Program |