Union Reservoir Nature Area
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.
Union Reservoir Water Levels Rising
Union Reservoir started 2025 at half capacity. Thanks to spring rains and flows from St. Vrain Creek, water levels have risen by one foot in early June, with another two feet expected by the end of the month. It’s still uncertain whether the reservoir will reach full capacity by the end of summer.
Swim Beach Opening Delayed for Safety
Following a safety review by Recreation staff, Park Rangers, and Risk Management, the City has delayed opening the Swim Beach, originally planned for Memorial Day weekend. As of June 6, water has not yet reached the swim area. Staff are monitoring conditions and will reassess weekly.
Why the Delay?
Low water levels have exposed parts of the old lakebed near the Swim Beach that still contain glass, fishing gear, and other debris from the reservoir’s past. Rangers have cleared the visible shoreline, but we can’t confirm that submerged areas are safe for swimmers.
Next Steps to Opening the Swim Beach
We’ll wait until the water rises enough to cover the cleaned lakebed and sandy beach. Once it’s safe, we’ll open a smaller swim area and expand it as water levels increase. Open Water Swims (OWS) remain postponed until water levels improve.
Solstice Swim Moving Forward
The Solstice Swim, hosted by MT Exile Productions on Sunday, June 22, will proceed as scheduled. Organizers will provide safety mats and course markings to assist racers through shallow water areas.
Boating and Fishing Updates:
• Be prepared to walk from the shore to the water – protective footwear is advised.
• Portions of the public floating dock are installed; water may be only 2 feet deep at the dock’s end.
• Shallow water depth conditions continue.
• Fishing piers remain set back from the water due to low levels.
Reservoir Access
Union Reservoir is open for:
- Boating
- Fishing
- Kayaking
- Paddleboarding
- Picnicking
- Dog beach use
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)
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