Nelsonville, located in Portage, Wisconsin, is home to a hydroelectric dam on the Tomorrow River. This historic dam, completed in 1855, serves multiple purposes including hydroelectric power generation and recreation. With a gravity dam type and a height of 14 feet, the Nelsonville dam has a low hazard potential and is classified as having a very high risk due to its age and structural condition, which has not been rated.

The dam has a storage capacity of 180 acre-feet and a drainage area of 69 square miles, with a maximum discharge of 1685 cubic feet per second. Despite its age, the Nelsonville dam is still in operation and is regulated by the Wisconsin Department of Natural Resources (WIDNR), which oversees its permitting, inspection, and enforcement. The dam's condition is currently not rated, and it has a 10-year inspection frequency to ensure its safety and functionality.

Water resource and climate enthusiasts will be intrigued by the historical significance and operational capabilities of the Nelsonville dam. Its location on the Tomorrow River, combined with its hydroelectric power generation and recreational uses, make it a key structure in the region. However, the dam's age and risk assessment highlight the importance of ongoing monitoring and maintenance to ensure its safety and efficiency in the face of changing environmental conditions.