Union Reservoir Nature Area

Overview

461 County Road 26, Longmont, CO 80504
303-772-1265
union@longmontcolorado.gov

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.

Before You Go – Water Access Updates

2/26/25:  Low Water Levels at Union Reservoir

Low water levels are affecting boating access to Union Reservoir. Water levels are down nearly ten feet lower than normal for this time of year. Due to a construction project upstream, water is not being released into Union until after its April completion.

Low water levels mean:
• Extended walking from shore to the waterline is required
• Boat docks do not extend into the waterline. Paved ramp does not extend to the waterline.
• Shallow water depth conditions exist
• Fishing piers are not near the waterline

Questions? Email Union@longmontcolorado.gov.

Find Out More

• Activities
• Fees and Hours
• Future enhancement plans for Union Reservoir recreation & complementary trail
• Get real-time estimated entry wait times & water temperature
• Purchase Union Season Passes Online
• Special Events
• Union Reservoir as a water supply resource for Longmont
• Union Reservoir Map (PDF)