East, also known as Agricultural #3 or Little Osner, is a private dam located in Jefferson County, Colorado, specifically in the city of Lakewood. Constructed in 1910 by designer Leonard Rice Costin, this earth dam stands at a height of 18 feet and has a storage capacity of 190 acre-feet. Its primary purpose is irrigation, with secondary purposes including recreation. The dam has a spillway width of 42 feet and a maximum discharge of 950 cubic feet per second, making it a critical structure for water management in the area.

With a high hazard potential and a satisfactory condition assessment as of May 2020, East is regulated by the Colorado Division of Water Resources and undergoes regular inspections and enforcement measures to ensure its safety and functionality. The dam has been modified over the years for structural and hydraulic improvements, with the most recent modifications occurring in 1973. Despite its moderate risk assessment rating, East plays a crucial role in managing water resources in the region and is equipped with emergency action plans to address any potential hazards or incidents that may arise. Water resource and climate enthusiasts will find East to be a fascinating example of the intersection between human engineering and natural water systems in the Rocky Mountain region.