Rat No. 1, also known as Enl of 301s, is a private earth dam located in Edgemont, South Dakota, along the West Fork Rat Creek. Completed in 1956, this irrigation dam stands at a height of 21 feet and has a hydraulic height of 16 feet. With a storage capacity of 191 acre-feet, Rat No. 1 serves the primary purpose of irrigation for the surrounding area.

Despite its age, Rat No. 1 has a low hazard potential and is currently in poor condition, as assessed in April 2017. The dam features a slide (sluice gate) outlet gate, with a spillway width of 50 feet for uncontrolled water release. Even though the risk assessment indicates a moderate level of risk (3), the dam is state-regulated and undergoes regular inspections, enforcement, and permitting to ensure its structural integrity and safety.

Located in Converse County, Wyoming, Rat No. 1 is within the jurisdiction of the State of Wyoming's regulatory agency (SEO). Congresswoman Liz Cheney (R) represents the area in Congressional District 00. Water resource and climate enthusiasts interested in the maintenance and monitoring of dams for irrigation purposes will find Rat No. 1's data informative and relevant to ongoing efforts in water management and safety.