Day Reservoir, located in Mulino, Oregon, is a private-owned water resource managed by the State of Oregon. Built in 1971, this Earth dam stands at 26 feet high and spans 290 feet in length, serving primarily for irrigation purposes. With a storage capacity of 12.2 billion gallons, it covers a surface area of 1.35 square miles and is fed by Milk Creek. The reservoir is regulated, inspected, and enforced by the Oregon Water Resources Department, ensuring its safe operation.

Despite its age, Day Reservoir maintains a significant hazard potential due to its structural integrity and emergency preparedness not being rated. The dam features a slide gate outlet system and has a maximum discharge rate of 48 cubic feet per second. Regular inspections are carried out every three years, with the last assessment conducted in November 2018. Although the reservoir does not have an Emergency Action Plan (EAP) in place, it remains a crucial water source for irrigation in the Clackamas County area, highlighting the importance of monitoring and managing its risks effectively to safeguard the surrounding community and environment.