Mason1 Dam, located in Norwalk, Iowa, is a private-owned structure regulated by the Iowa Department of Natural Resources. Built in 2004, this earth dam stands at a height of 24 feet and has a storage capacity of 289 acre-feet. The dam serves the primary purpose of water retention for the Tr- North Branch river/stream, with a normal storage capacity of 163 acre-feet and a surface area of 23.5 acres.

With a low hazard potential and a moderate risk assessment rating, Mason1 Dam has not been fully assessed for its condition but is noted to be in a satisfactory state. The spillway type at the dam is uncontrolled, with a width of 20 feet. Despite being a private-owned structure, the dam meets state regulations for permitting, inspection, and enforcement. The dam is situated within the Kansas City District and falls under the jurisdiction of the Iowa DNR, ensuring its compliance with safety and environmental standards.

Water resource and climate enthusiasts will appreciate Mason1 Dam for its role in water management and flood control in the region. The collaboration between the NRCS and the private landowner in designing and maintaining the dam showcases a successful partnership in sustainable water resource management. Its location in Madison County, Iowa, adds to the significance of Mason1 Dam in supporting the local ecosystem and contributing to the overall water infrastructure in the area.