Lost Lake, located in Mesa, Colorado, is a privately owned Earth dam built in 1922 for irrigation purposes. The dam stands at a height of 12 feet with a hydraulic height of 11 feet and a length of 280 feet, providing a storage capacity of 126 acre-feet. The reservoir covers an area of 26 acres and is fed by the Bull Creek-TR stream, with a maximum discharge capacity of 44 cubic feet per second.

Despite its age, Lost Lake's hazard potential is classified as low, with a fair condition assessment as of 2010. The dam features an uncontrolled spillway and one slide gate outlet, with inspection and maintenance carried out by the Colorado Division of Water Resources. The surrounding area is at a moderate risk level, requiring ongoing risk management measures to ensure the safety and stability of the structure.

Lost Lake is a historic dam that continues to serve its intended purpose of irrigation while maintaining a relatively low hazard potential. With its stone core and rock-soil foundations, the dam stands as a testament to early 20th-century engineering. As water resource and climate enthusiasts, understanding and preserving the infrastructure of Lost Lake is crucial for maintaining water supply and mitigating risks in the face of changing environmental conditions.