Thomson Dam, located in Defiance, Iowa, was completed in 1975 and is primarily owned and regulated by private entities. The dam, designed by USDA NRCS, serves multiple purposes such as fire protection, stock, and small fish pond. With a height of 27 feet and a length of 610 feet, Thomson Dam has a storage capacity of 109 acre-feet and covers a surface area of 6.3 acres, with a drainage area of 0.46 square miles.

The dam, situated on TR-WILLOW CREEK, is classified as an Earth dam with a low hazard potential and a moderate risk assessment. Although the condition of the dam is not rated, it undergoes state inspection, regulation, and enforcement by the Iowa Department of Natural Resources. Thomson Dam features an uncontrolled spillway and has not been modified in recent years. Despite the lack of detailed risk management measures, the dam's operational capacity and potential emergency response have not been fully assessed.

For water resource and climate enthusiasts, Thomson Dam serves as a vital structure for water management in Crawford County, Iowa. With its strategic location and multi-purpose functionality, the dam plays a crucial role in providing fire protection and sustaining local wildlife. The dam's design by USDA NRCS ensures its structural integrity, while ongoing state oversight guarantees compliance with regulatory standards. As a key feature within the Rock Island District, Thomson Dam contributes to the overall water infrastructure and ecosystem resilience in the region.