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 a construction project upstream, water will not be released into Union Reservoir until the project is completed sometime in April 2025.

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)