Lower Lake Mary, located in Coconino, Arizona, is a federal water supply reservoir managed by the USDA Forest Service. Built in 1907, this earth dam structure stands at 33 feet high with a storage capacity of 22,400 acre-feet and a surface area of 910 acres. The reservoir primarily serves as a water supply source but also supports fish and wildlife habitats, recreation activities, and flood control along Walnut Canyon.

With a high hazard potential, Lower Lake Mary has a moderate risk rating, indicating a need for ongoing monitoring and management. The dam features an uncontrolled spillway and a spillway width of 75 feet to manage maximum discharge levels of up to 3,298 cubic feet per second. Despite its condition being currently unrated, the reservoir's inspection frequency of one year suggests regular assessments to ensure the safety and functionality of the structure. For water resource and climate enthusiasts, Lower Lake Mary offers a fascinating case study of a historic dam supporting multiple purposes in a scenic natural setting within the Walnut Canyon area.