Oberon Lake No. 1, also known as Hay's Lake or Lower Oberon, is a vital water resource located in Jefferson County, Colorado. Owned by the local government, this earth dam structure was completed in 1887 with the primary purpose of flood risk reduction along the Ralston Creek-OS. The dam stands at a height of 20 feet with a hydraulic height of 20 feet and a structural height of 28 feet, providing a maximum storage capacity of 69 acre-feet.

This historic water infrastructure covers a surface area of 3 acres and has a normal storage capacity of 6 acre-feet, serving as a low hazard potential structure with a satisfactory condition assessment. Despite its age, Oberon Lake No. 1 continues to be regulated and inspected by the Colorado Department of Water Resources, ensuring its continued functionality and safety. With a moderate risk assessment rating, the dam is equipped with an uncontrolled spillway and last underwent inspection in October 2012.

For water resource and climate enthusiasts, Oberon Lake No. 1 presents an intriguing blend of history, engineering, and environmental stewardship. As a crucial component in flood risk reduction efforts in the region, this earth dam serves as a testament to the importance of sustainable water management practices. With its low hazard potential and satisfactory condition, Oberon Lake No. 1 remains a key player in water resource management in the picturesque city of Arvada, Colorado.