Union Reservoir
![View of swim beach at Union Reservoir](https://longmontcolorado.gov/wp-content/uploads/2024/08/Union_swim_beach.jpg)
Overview
Union Reservoir Nature Area
461 County Road 26, Longmont, CO 80504
303-772-1265
Union Reservoir is a 736 acre body of water providing many outdoor recreational activities. Originally called Calkins Lake, the reservoir was carved out during the last glacial age and is one of only a few natural lakes in Colorado. In 1903, the Union Ditch Company began drilling a tunnel to release water into the St. Vrain Creek. According to Colorado water law, that made Union a true reservoir.
The Reservoir is located approximately 7 miles west of I-25.
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