Johnson Dam in Washington County, Iowa, is a private-owned structure designed by USDA NRCS with a primary purpose of grade stabilization. Completed in 2005, the earth dam stands at a height of 25 feet and spans 500 feet in length. The dam has a storage capacity of 159 acre-feet, with a surface area of 12 acres and a drainage area of 0.41 square miles.

Located in Wapello along the Tr- Long Creek, Johnson Dam serves as a fish and wildlife pond in addition to its grade stabilization function. It is regulated by the Iowa Department of Natural Resources and undergoes regular state inspection, enforcement, and permitting. With a low hazard potential and current condition assessment as "not rated," the dam contributes to the conservation and management of water resources in Louisa County.

Although specific details on spillway type and outlet gates are not provided, Johnson Dam plays a crucial role in holding back water flow and preventing erosion in the area. With its strategic placement and design, the dam supports environmental conservation efforts and ensures the sustainable use of water resources for the community.