Johnston Dam, located in Marion, Iowa, near the Red Rock Reservoir, was completed in 1973 by the USDA NRCS and serves as a private water resource for fire protection, stock, and small fish ponds. With a dam height of 36 feet and a length of 320 feet, the earth dam has a storage capacity of 75 acre-feet and covers a surface area of 5.3 acres. The dam is regulated by the Iowa Department of Natural Resources and has a low hazard potential, with a moderate risk assessment rating.

Despite being a relatively small dam, Johnston Dam plays a crucial role in water management and conservation in the region. It is designed to provide essential water resources for various purposes, including recreation, in addition to its primary functions. The dam's location on TR-Ballard Creek ensures a reliable water source for the surrounding area, contributing to the sustainability and resilience of the local ecosystem.

As a key component of the water infrastructure in the area, Johnston Dam is subject to regular inspections and regulatory oversight to ensure its safety and functionality. While it has not been rated for its condition, the dam is considered to have moderate risk potential, emphasizing the importance of continued monitoring and maintenance to prevent any potential hazards. With its strategic positioning and crucial role in water resource management, Johnston Dam remains a significant asset for the community and the environment.