Hannen Lake Dam, located in Benton County, Iowa, is a local government-owned structure designed by the Howard R Green Co. The dam, completed in 1959, serves a primary purpose of recreation and has a normal storage capacity of 390 acre-feet. With a dam height of 35 feet and a length of 600 feet, it impounds the waters of TR-COON CREEK to create a surface area of 39 acres for recreational activities.

Managed by the Iowa Department of Natural Resources, Hannen Lake Dam is regulated, permitted, inspected, and enforced by state agencies to ensure its safety and compliance with standards. The dam has a low hazard potential and a satisfactory condition assessment as of the last inspection in June 2019. Despite its low risk, the dam is considered to have a moderate overall risk level, indicating the need for continued monitoring and risk management measures.

Situated in the Detroit District of the US Army Corps of Engineers, Hannen Lake Dam has not been modified in recent years and does not feature significant outlet gates or locks. While the dam's spillway is uncontrolled with a width of 5 feet, it has not experienced maximum discharge events. Overall, Hannen Lake Dam provides a crucial recreational resource for the community while maintaining a focus on safety and risk management in its operation and maintenance.