Lower Monumental Lock And Dam

About Lower Monumental Lock And Dam

The primary purpose of Lower Monumental Lock And Dam is navigation. The dam maintains water levels sufficient for boat and barge traffic, supporting commercial or recreational navigation on the waterway. The dam is owned by Usace - Walla Walla District (federal). It impounds the Snake River near Pasco.

The dam stands 226 feet tall and stretches 3,800 feet across, creates a reservoir covering 6,590 acres, has a maximum storage capacity of 432,000 acre-feet, and collects water from a drainage area of 108,500 square miles. Completed in 1969, the structure is well into its service life at over 50 years 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. An emergency action plan is in place for this dam. The most recent inspection on record was 10/29/2025.

At 226 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 Washington dam safety program can provide more specific information about emergency planning for this structure.

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