Green Swamp #1 Dam
Green Swamp #1 Dam is an earth dam located in Passaic County, New Jersey, built in 1926. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Green Swamp #1 Dam
The primary purpose of Green Swamp #1 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 Post Brook.
The dam stands 29 feet tall and stretches 640 feet across, creates a reservoir covering 2,400 acres, has a storage capacity of 41,700 acre-feet, and collects water from a drainage area of 94 square miles. Completed in 1926, 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. 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.
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 | Post Brook |
| Coordinates | 41.04130, -74.32320 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 29 ft |
| Dam Height | 29 ft |
| Dam Length | 640 ft |
| Year Completed | 1926 (100 years old) |
Storage & Hydraulics
| NID Storage | 41,700 acre-ft |
| Normal Storage | 41,700 acre-ft |
| Surface Area | 2,400 acres |
| Drainage Area | 94 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 | NJ00209 |
| Federal ID | NJ00213S001 |
| More Info | State Dam Safety Program |