Marfell Lake No. 1, located in Boulder, Colorado, is a private earth dam that was completed in 1880 for irrigation purposes. With a height of 12 feet and a length of 2700 feet, the dam has a storage capacity of 140 acre-feet and a surface area of 19 acres. While primarily used for irrigation, the lake also offers recreational opportunities in the area.

The dam, regulated by the Colorado Department of Water Resources, has a low hazard potential and a moderate risk assessment rating. Despite not being rated for its condition, regular inspections are conducted, with the last one taking place in February 1995. The spillway type is uncontrolled, with a width of 25 feet, and the maximum discharge capacity is 200 cubic feet per second.

Water resource and climate enthusiasts will be intrigued by Marfell Lake No. 1, as it serves as a historical and functional irrigation structure in the region. Its significance lies not only in its practical use for water management but also in providing a recreational space for the local community. With its unique features and regulatory oversight, this dam offers a fascinating insight into water resource management practices in Colorado.