Tremaine Reservoir, also known as Hay Lake, is a Federal-owned water storage structure located in Coconino County, Arizona. Built in 1952 by the USDA Natural Resource Conservation Service, the primary purpose of the reservoir is irrigation, with additional benefits for fire protection, stock watering, and fish and wildlife habitat. The dam is an earth type structure with a height of 30 feet and a length of 1935 feet, providing a storage capacity of 8000 acre-feet and a surface area of 265 acres.

Situated on the Jacks Canyon Tributary in the Two Guns area, Tremaine Reservoir plays a crucial role in water resource management and conservation efforts in the region. With a low hazard potential and fair condition assessment as of August 2020, the reservoir is maintained and regulated by the Forest Service to ensure safe operations. The risk assessment for the dam is categorized as moderate, indicating the need for ongoing monitoring and risk management measures to protect the surrounding communities and environment.

Despite its relatively small drainage area of 17 square miles, Tremaine Reservoir has a maximum discharge capacity of 7647 cubic feet per second, with an uncontrolled spillway width of 231 feet. Regular inspections every 10 years help to assess the structural integrity and safety of the dam, with the last assessment conducted in August 2020. As a valuable resource for irrigation and conservation in the region, Tremaine Reservoir continues to play a vital role in water management and climate resilience efforts.