Visit Union Reservoir this Season

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 River. According to Colorado water law, that made Union a true reservoir. Today, visitors to Union Reservoir can enjoy fishing, swimming, paddleboarding, wakeless boating,  windsurfing and picnicking. The Reservoir is located approximately 7 miles west of I-25.


Mandatory boat inspections are required before launching.  Inspections hours are from 7 a.m to 7 p.m. daily.

Water Conditions

Please contact the Union Reservoir Office for current information.

Paddleboard & Kayak Rentals

Rocky Mountain Paddleboard offers rentals of paddleboards and kayaks at Union Reservoir. Please visit their website to make a reservation and find additional information.

Sailing Club

Union Sailing Club is one of Colorado’s largest and most active sailing clubs with weekly racing in the spring, summer and fall. Several regattas, social events, youth activities and clinics open to the general sailing public are also hosted each year. Instruction is also offered. Club boats are available on a limited basis for rental to experienced sailors. For more information, please visit the Union Sailing Club website.

Rocky Mountain Paddleboard offers Stand Up Paddleboarding (SUP), SUP Yoga, Full Moon Paddles and kayak rentals. Photo: Lisa Fierer



A dog-friendly beach is located on the south side of the reservoir. Dogs are allowed off leash and may swim in this designated area. Dogs must be leashed in all other areas of the park.


The Reservoir is fast becoming one of Colorado’s finest walleye fisheries. Walleye 17-24 inches are common. In recent years, Union Reservoir has become the hotspot for fly fishermen who enjoy the thrill of catching the hard-fighting carp. In addition, a healthy population of trout, crappie, catfish, bass, sunfish, wiper and tiger muskie provide a quality fishing experience. Fishing is available along the majority of the shoreline or from a boat. Colorado fishing regulations are enforced and a fishing license is required. A fish cleaning station and handicapped accessible fishing pier are provided for your convenience.

Union Reservoir offers fishing from the majority of the shoreline or from a wakeless boat. Photo: Colorado Fly Fishing Reports.


Numerous picnic sites with a table and grills are located throughout the park. Both group and individual sites are available on a first come, first served basis. For a fee of $75 a day, you may reserve the main picnic area or the shelter (additional gate fee per vehicle is required). There are picnic tables and barbecues set up in prime locations for use as well. Beverages up to 3.2{5f17c0b77576b4418c7f5b84070ee54dec816ea05020410e2b3771abf72ce4bb} alcohol are permitted in the main picnic area or the shelter with a permit. The fee for an alcohol permit is an additional $75. For online shelter reservations, click here.


Union Reservoir’s sandy beaches provide a gathering spot for young and old alike. Lifeguards are stationed at the beach for safety. Swimming is allowed during posted hours only. A sand volleyball court, picnic shelter and playground are located near the beach for your enjoyment. Temporary loading and unloading is permitted along the beach for easy access, with parking in the paved lot.

Children will enjoy the playground that is located near the beach



One of the best windsurfing spots in northern Colorado! Easy water-front access with great conditions creates a windsurfer’s paradise.


Triathlons  –  Access to the Reservoir may not be possible until after 11:30 a.m.

  • Dates:   May 20, July 30, September 24, 2017

Kinetics Sculpture Race & Festival  –  Season passes are not valid for Kinetics – $10 Special Event Fee

  • Date:    June 24, 2017

Full Moon Paddle – Season passes are not valid for Full Moon Paddle – $8 per person Special Event Fee

  • Dates:  July 9, August 7, September 6, October 5, 2017, 7 – 10 p.m.

Daily vehicle fee – $8
Trailered Boat – $8
Bicycle/Walk-in – $2 per person
Annual Pass – $60/resident, $75/non-resident
Colorado Disabled Veterans (with current Disabled Veteran license plate) – Free

March 1 – April 30 – 7 a.m. – 7 p.m.
May 1 – Labor Day – 6 a.m. – 9 p.m.
September 6-30 – 7 a.m. – 8 p.m.
October 1-31 – 8 a.m. – 5 p.m.
November 1- February 28 – Sunrise-Sunset (Walk-ins only, daily admission fees apply)

For swim beach and open water hours, please click here.


Union Reservoir
461 County Road 26
Longmont, Colorado 80504