Lake Mills, also known as Rock Lake, is a picturesque reservoir located in Jefferson County, Wisconsin. Owned and regulated by the local government, this gravity dam was completed in 1865 for the primary purpose of recreation. With a height of 17.2 feet and a storage capacity of 28,330 acre-feet, the dam sits on Rock Creek and covers a surface area of 1,371 acres.

Despite its age, Lake Mills remains in satisfactory condition with a high hazard potential due to its location and structural specifications. Regular inspections are conducted by the Wisconsin Department of Natural Resources, with the last assessment taking place in October 2019. The dam has a controlled spillway and a maximum discharge of 115 cubic feet per second, serving as a vital resource for the community while also posing a very high risk in the event of a failure.

In recent years, Lake Mills has undergone modifications in 1962 and 2016 to ensure its continued safety and functionality. With its scenic surroundings and recreational opportunities, this reservoir serves as a key feature in the region's water resource management efforts, attracting enthusiasts interested in both water conservation and climate resilience.