Thayer No. 1 is a privately owned earth dam located in Park, Wyoming, specifically on the Greybull River off Carter Mountain. Completed in 1935, this irrigation structure stands 13 feet tall and has a hydraulic height of 7 feet, with a length of 120 feet. It has a storage capacity of 69 acre-feet and a surface area of 17 acres, serving the purpose of irrigation for the surrounding area.

Despite its age, Thayer No. 1 has a low hazard potential and is currently in fair condition, as assessed during the last inspection in September 2019. The dam is under state jurisdiction and regulation, with permitting, inspection, and enforcement processes in place through the State Engineer's Office. In the event of an emergency, the dam has one valve outlet gate and an uncontrolled spillway with a width of 40 feet.

Thayer No. 1 poses a moderate risk level, but with proper risk management measures in place, it continues to provide essential irrigation functions for the region. As water resource and climate enthusiasts, understanding and monitoring the condition of dams like Thayer No. 1 is crucial for ensuring the safety and sustainability of our water infrastructure.