Longwood Lake Dam

About Longwood Lake Dam

The primary purpose of Longwood Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Jersey City Municipal Utilities Authority (local government). It impounds the Rockaway River near Jefferson.

The dam stands 22 feet tall and stretches 91 feet across, creates a reservoir covering 43 acres, has a maximum storage capacity of 351 acre-feet, and collects water from a drainage area of 19 square miles. Completed in 1898, 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 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 03/21/2024.

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.

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