Onion River

About Onion River

The primary purpose of Onion River is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Village Of Waldo (local government). It impounds the Onion near Waldo.

The dam stands 15 feet tall and stretches 300 feet across, creates a reservoir covering 40 acres, has a maximum storage capacity of 200 acre-feet, and collects water from a drainage area of 22 square miles. Completed in 1856, the structure is one of the older dams in the region, with over a century and a half 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 fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 08/27/2020.

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 Wisconsin dam safety program can provide more specific information about emergency planning for this structure.

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