Union Reservoir

Union Reservoir is a 736-acre body of water providing recreational opportunities all-year round for visitors and residents alike.

Cover Photo: Paul Marcotte

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. Spend the day relaxing on the beach, letting your furry friend swim at the dog beach, or try your hand at windsurfing, paddleboarding, or sailing! The Reservoir is located approximately 3 miles from Downtown Longmont and 7 miles west of I-25  making it a convenient hub for water activities on your next trip to Longmont!

Fees and hours can be found here.  

#KnowBeforeYouGo  -Due to its popularity, Union Reservoir may have a line to enter, especially on weekends and holidays.  Plan accordingly and also check the real-time estimated entry wait times.

Activities offered at Union Reservoir include:

Boating: Wakeless boating is allowed on the reservoir but jet skis are prohibited.

Paddleboard & Kayak Rentals: Rocky Mountain Paddleboard offers rentals of paddleboards and kayaks at Union Reservoir. Please click here for more information.

Fishing: Union Reservoir is fast becoming one of Colorado's finest Walleye fisheries. Walleye 17 to 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.

Swim Beach: Union Reservoir's sandy beaches provide a gathering spot for all ages. Relax on the sand for a day of fun in the sun. Lifeguards are stationed at the beach for safety. Swimming is allowed during posted hours only (see Hours).  Check water temperature.

Open Water Swim: Swimming outside of the designated swim beach is considered open water swimming; it is only permitted during posted Open Water Swim hours when lifeguards are on duty (see Hours).  Union Reservoir season passes or recreation facility passes are NOT accepted as a substitute for Open Water Swim (see Fees).

Dog Beach: A dog off-leash area is located on the south side of the reservoir. Dogs are allowed off-leash and may swim in this designated area. A great place to take Fido for a summer getaway!

Picnicking: Numerous picnic sites with tables and grills are located throughout the park. Both group and individual sites are available on a first-come, first-served basis. For a fee, 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.  Contact the Union Reservoir Office to reserve.  

Special Events: Union Reservoir is commonly home to triathlons, community festivals and boating events. During such events, there may be special fees required at the gate. View our Special Events - Union Reservoir webpage to see upcoming events.

Winter Activities: During winter, Union is open from sunrise to sunset. Daily admission fees still apply, and access is limited to walk-in. No boating or ice fishing is allowed during the winter.

Windsurfing: One of the best windsurfing spots in northern Colorado! Easy waterfront access with great conditions creates a windsurfer's paradise.

Sailing: 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 go to the Union Sailing Club website.



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