Johnston Dam, located in Davis County, Iowa, was completed in 1972 and serves multiple purposes including fire protection, stock watering, and serving as a small fish pond. Owned privately, the dam is regulated by the Iowa Department of Natural Resources and is subject to state inspection and enforcement. With a height of 25 feet and a length of 510 feet, Johnston Dam has a storage capacity of 77 acre-feet, with a normal storage level of 48 acre-feet.

Situated on TR-Carter Creek, Johnston Dam has a surface area of 5.6 acres and drains a 0.17 square mile area. The dam's hazard potential is rated as low, with a moderate risk assessment score of 3 out of 5. The spillway type is uncontrolled, and the dam is primarily constructed of earth with a soil foundation. While the dam has not been assigned a condition assessment rating, it is noted to be in a not rated condition. Overall, Johnston Dam serves as a vital resource for water management and conservation in the area, contributing to the local ecosystem and providing essential services to the community.