Green Swamp #4 Dam
Green Swamp #4 Dam is a concrete dam located in Passaic County, New Jersey, built in 1925. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Green Swamp #4 Dam
The primary purpose of Green Swamp #4 Dam 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 North Jersey District Water Supply Commission (state). It impounds the Wanaque River.
The dam stands 65 feet tall and stretches 300 feet across, creates a reservoir covering 2,310 acres, has a storage capacity of 81,730 acre-feet, and collects water from a drainage area of 90 square miles. Completed in 1925, 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 satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 10/16/2024.
At 65 feet, this dam is taller than 96% 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 New Jersey 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 | New Jersey |
| County | Passaic |
| River/Stream | Wanaque River |
| Coordinates | 41.04032, -74.31135 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 65 ft |
| Dam Height | 65 ft |
| Dam Length | 300 ft |
| Year Completed | 1925 (101 years old) |
Storage & Hydraulics
| NID Storage | 81,730 acre-ft |
| Normal Storage | 81,730 acre-ft |
| Surface Area | 2,310 acres |
| Drainage Area | 90 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | North Jersey District Water Supply Commission |
| Owner Type | State |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/16/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | NJ00212 |
| Federal ID | NJ00213S004 |
| More Info | State Dam Safety Program |