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

Spring 2025:  Low Water Levels at Union Reservoir

Water levels at Union Reservoir are nearly ten feet lower than normal for this time of year and are affecting boating access. Due to an inlet diversion project upstream, water will not be released into Union Reservoir until late May 2025. Water levels are expected to return to normal sometime in June.

Low water levels mean:
• Extended walking from shore to the waterline is required
• Boat docks and the paved ramp do not extend into 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)