Union, also known as Calkins Lake, is a privately owned dam located in Weld County, Colorado, near the city of Platteville. This earth-type dam was completed in 1902 and serves primarily for irrigation purposes, with additional functions including fish and wildlife pond creation and recreational activities. The dam stands at a height of 33 feet and has a storage capacity of 16,250 acre-feet, providing vital water resources for the surrounding area.

Managed by the Colorado Department of Water Resources, Union Dam is subject to state regulations, inspections, and enforcement to ensure its safe operation. With a significant hazard potential and a moderate risk assessment rating, the dam has a satisfactory condition assessment as of August 2019. The spillway, designed as uncontrolled, has a width of 900 feet to accommodate a maximum discharge of 14,925 cubic feet per second, protecting downstream areas in case of overflow.

Despite its age, Union Dam remains a critical infrastructure for water management in the region, showcasing the importance of proper maintenance and regulation to mitigate potential risks and ensure the safety of surrounding communities. With its historical significance and ongoing role in providing essential water resources, Union Dam stands as a testament to the intersection of water management, climate resilience, and environmental stewardship in Colorado.