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Union Reservoir currently remains open to the public during the State of Colorado's Stay at Home Order.

  • Fishing, boating, dog beach and paddle boarding are open.
  • Playground and shelter are closed.
  • Boat inspections are available between 8 a.m.-5 p.m. daily. Please remain in your vehicle while your boat is being inspected.


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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Special Events

Fees and Hours

Union Reservoir as a water supply resource for Longmont

Future enhancement plans for Union Reservoir recreation & complementary trail

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