Johnston Dam, located in Lynnville, Iowa, is a private dam designed by NRCS with a height of 30 feet and a length of 527 feet. Completed in 2005, the dam serves multiple purposes including fire protection and creating a small fish pond. With a storage capacity of 193 acre-feet, the dam regulates the flow of Turner Creek and covers a surface area of 10.9 acres.

Managed by the Iowa DNR, Johnston Dam is state-regulated with inspection, permitting, and enforcement protocols in place. The dam has a significant hazard potential but is currently rated as "Not Rated" in terms of condition assessment. While the risk assessment is moderate, with a score of 3, there are no specific risk management measures or emergency action plans in place as of the last data update in April 2021.

Johnston Dam plays a vital role in water resource management in Jasper County, Iowa, contributing to fire protection and supporting local wildlife. As a private structure with state oversight, the dam underscores the importance of sustainable infrastructure to ensure the safety and well-being of the community and surrounding environment in the face of climate variability and water resource challenges.