Mackay, a privately owned dam located in Idaho, was completed in 1918 and sits on the Big Lost River Sinks. This rockfill dam stands at a height of 75.2 feet with a storage capacity of 45,000 acre-feet and a surface area of 1,392 acres. With a drainage area of 788 square miles, the dam has a maximum discharge rate of 7,000 cubic feet per second.

Despite being classified as having a high hazard potential, Mackay is currently in fair condition following its last inspection in October 2019. The dam features an uncontrolled spillway and a slide (sluice gate) outlet gate. Its emergency action plan (EAP) status is not specified, and there have been no inundation maps prepared. The risk assessment for Mackay indicates a moderate risk level (3), suggesting a need for ongoing monitoring and risk management measures to ensure the safety and integrity of the structure.

For water resource and climate enthusiasts, Mackay presents an intriguing case study in dam infrastructure management and risk assessment. Its location in the scenic Custer County, Idaho, surrounded by the natural beauty of the Big Lost River Sinks, underscores the importance of balancing water resource development with environmental conservation and safety considerations. As discussions around climate change and water scarcity continue to evolve, understanding the condition and risk profile of dams like Mackay becomes increasingly vital for sustainable water management practices in the region.