Four miles east of downtown Longmont, the Union Reservoir Nature Area is a popular outdoor recreation destination centered around the 736-acre Union Reservoir. Located in southwestern Weld County, the reservoir and nature area are owned by the City of Longmont and open daily to the public for a small entry fee.
In the summer, the easily accessible lake is popular for boating, fishing, and swimming. As a historically important feature of the area, water from the Union Reservoir is primarily used to irrigate farms between Longmont and Greeley found along the South Platte River.
History of the Union Reservoir (Calkins Lake)
Originally, Calkin’s Lake (as it was formerly known) existed as a natural, glacially-formed body of water in a depression that was likely enlarged over time by herds of bison. In 1903, the lake became a “reservoir” by definition when the Union Ditch Company drilled a tunnel into the reserve, releasing water into St. Vrain Creek to supplement irrigation.
For nearly 100 years, the land occupied by and surrounding Calkin’s Lake was owned by the private Union Reservoir Company. In 1986, The City of Longmont purchased the reservoir to secure a controlling interest (52%) of the Union Reservoir Company. By 2011, the city-owned 85% of the company’s shares.
Since the transfer of ownership, the City of Longmont has implemented various versions of the Union Reservoir Recreational Master Plan to increase the surface area, storage capacity, and recreational potential of the water. The largest goal of the project is to increase the size of the reservoir.
Currently, Longmont is working to purchase the land around the reservoir necessary to accommodate the expansion from the current 12,000 acre-feet to a total of 32,000 acre-feet. On a willing seller/willing buyer basis, the process began in 1996, and the city has purchased approximately 265 acres of property surrounding the water so far.
In 2022, The Union Reservoir Trail has been funded for construction, which will create and connect paved and soft-surface paths for visitors to circumnavigate the water.
Activities near Union Reservoir
The City of Longmont opened recreational use of Union Reservoir/Calkin’s Lake to the public in 1991 and continuous improvements have made it a popular destination for easily accessible outdoor fun. For frequent visitors, season passes are available with varying rates for residents, non-residents, 1st vehicle, 2nd vehicle, seniors, boats, school buses, and commercial operators.
Birding: The Union Reservoir is a great spot for spotting water birds like ducks, grebes, gulls, godwits, and even two distinct species of loons. Driving by, vehicular birdwatching is possible along County Rd 26 to avoid the crowds or park entrance fees.
Boating: Non-motorized boating is a popular activity at the Union Reservoir, with paid seasonal boat storage available onsite. The wakeless waters create generally good conditions for paddleboarding, kayaking, canoeing, and windsurfing.
Seasonal rentals for both kayaks and stand-up paddleboards are available on the south shore of the water through Rocky Mountain Paddleboard. The City of Longmont also hosts many fun special boating events such as the famous evening full moon paddles.
Camping: Prior to 2018, a campground occupied a small portion of the Union Reservoir Nature Area. The space has now been reconfigured to better accommodate day-use activities, and thus camping is no longer available. As such, the park now closes to the public daily, an hour after sunset.
Fishing: With a valid Colorado fishing license, shore, boat, and pier fishing are permitted at the Union Reservoir. Easily accessible for all mobility levels, anglers of every age can enjoy the lake’s healthy population of catchable fish.
Beyond Colorado’s classic trout, Union Reservoir offers opportunities to bag carp, walleye, catfish, wiper, bass, sunfish, tiger muskie, and more. If you are planning to take your catch home for dinner, visitors are encouraged to use the fish cleaning station provided near the pier.
Picnicking: On and around the sandy beaches of Calkin’s Lake, picnics are very popular in the Union Reservoir Nature Area. With plenty of shade available, there are many first-come, first-served picnic tables with BBQ grills and grassy areas to enjoy a meal or snack in the open air.
Free for visitors to use, seasonal restrooms and drinking water fountains are also available around the picnic areas, swim beach, and dog park. If you’re planning an event or party, Union Rsevoir’s large picnic shelters can be reserved for full and half-day periods, through the City of Longmont.
Swimming: With a lifeguard on duty, swimming is permitted in the Union Reservoir within the roped-off area at the sandy swim beach. Pool toys are allowed at the discretion of the lifeguard, and large inflatables that are not Coast Guard approved (i.e. inflatable tubes and chairs) are not permitted to join the kayaks and canoes outside of the swim area.
The City of Longmont also hosts lifeguard-protected Open Water Swim Sessions where visitors can enjoy long-distance swimming for a small fee during designated hours. Typically held on Tuesday and Wednesday evenings as well as Friday and Saturday mornings, frequently registered participants are no longer charged a fee after their 15th open swim of the season.
Union Reservoir Accessibility
Less than 10 minutes from the center of Longmont, the Union Reservoir Nature Area is easily accessible for visitors from Denver, Boulder, Fort Collins, and other populous Front Range cities. From East County Line Road north of State Highway 119 (E Ken Pratt Blvd), turn onto County Rd 26 to head east. Drive half of a mile towards the south shore of the water and take a left at the sign for the Union Reservoir.
During peak seasons and busy hours, it is not uncommon for a line to form at the entry to the Union Reservoir Nature Area. Once you’ve entered the gate, there is ample room for parking with two large long-term lots and shoreside spaces designed to assist in boat loading and unloading.
If you plan to bring the four-legged members of your family, there is an off-leash dog park on the south side of the water. Pets are allowed to swim in this designated location but are limited to leash-only travel in all other parts of the nature area.
Address: 461 County Rd 26, Longmont, CO 80504
County: Weld County
Hours: An hour before sunrise to an hour after sunset
Fees: Various daily fees for vehicles, boats, and walk-ins/bikes. Season passes and boat storage are available.
Master Plan Map: longmontcolorado.gov/…