Main, also known as Big Osner, is a private water resource located in Jefferson County, Colorado. Built in 1908 for irrigation purposes, this Earth-type dam stands at a height of 45 feet and has a storage capacity of 1320 acre-feet. With a spillway width of 60 feet and a maximum discharge of 700 cubic feet per second, Main plays a crucial role in managing water flow and storage in the region.

The dam is state-regulated by the Colorado Department of Water Resources, ensuring that it is regularly inspected, maintained, and enforced for safety and compliance. Despite its high hazard potential, Main has been assessed as satisfactory in condition, with a moderate risk level of 3. Additionally, the dam has a history of being updated and meeting regulatory guidelines, showcasing a commitment to responsible water management and risk mitigation in the face of changing climate patterns and water resource challenges.

Located in Lakewood, Main serves not only for irrigation but also for recreational purposes, highlighting its multi-functional role in the community. With its historical significance and essential contribution to water supply and management, Main stands as a testament to the importance of sustainable water resource practices in the face of climate variability and increasing water demands.