Boulder Reservoir: Swimming, Boating and Trails Near North Boulder

Mar 24, 2026 / Oct 4, 2026 · 7 min read · Outdoor Activities 80304 Boulder Colorado Swimming Kayaking Cycling ·

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Boulder Reservoir: The City's Lake, Northeast of North Boulder

Boulder Reservoir is a 700-acre lake on the plains northeast of Boulder. The City of Boulder owns and manages it. It stores water for drinking and for farm irrigation, and it is also the city's biggest place to swim, boat and fish. From North Boulder it is east across town.

Where is it? 5275 Reservoir Rd., Boulder, CO 80301 — on the northeast side of Boulder.

How the Reservoir Was Built

The city's history page tells the story. The city bought land from the Axelson family's dairy farm and started building on May 1, 1954. The work was finished on Feb. 11, 1955, and that April the reservoir began to fill with water from the Colorado-Big Thompson Project, through what is now the Boulder Feeder Canal. It cost $1,158,027.

The lake was built to store water, but people came to play right away. Two months after it filled, 75 tons of sand were brought in to make a beach on the southeast shore. On the first Fourth of July, in 1955, more than 1,400 cars paid 25 cents each to get in. The first boating licenses were sold that August.

In the early 1980s, after voters passed a city bond, the beach was moved to the more sheltered southwest corner of the lake, where it is today. The site got running water for the first time, and many of today's buildings went up.

Water for the City

The reservoir still does its first job. It supplies about 20 percent of Boulder's drinking water. Between 80 and 90 percent of its water comes through the Boulder Feeder Canal; the rest comes from seasonal creeks and ditches. It holds up to 13,270 acre-feet. It is usually full by June and drawn down to about half by September. The Northern Colorado Water Conservancy District, known as Northern Water, operates and maintains the reservoir and has the right to one-third of its working capacity. Its water comes from Carter Lake through the St. Vrain Supply and Boulder Feeder canals. Water from the reservoir goes to Boulder and to irrigated farms and ranches in Boulder and Weld counties.

Northern Water gives these numbers: 700 surface acres, about 4 miles of shoreline, and a greatest depth of 28 feet. Boulder Reservoir is one of the three end-point reservoirs of the Colorado-Big Thompson Project, which brings water from the Western Slope under the mountains; the other two are Horsetooth Reservoir and Carter Lake.

Swimming and the Beach

The city says the reservoir has one of the largest lifeguarded beaches in Colorado. The swim area is open from Memorial Day weekend to Labor Day, usually from 10 a.m. to 6 p.m. On Thursdays it closes at 5:30 p.m. for the weekly Stroke & Stride event. In October 2026 it was closed for the season and set to reopen in late May 2027.

Some rules to know:

You may swim only inside the marked swim area, and only when lifeguards are on duty. The lifeguards are certified by the American Red Cross.
The swim area opens only when the water is warm enough: at least 60°F for the shallow part and 64°F for the whole area.
Children under 13 must be watched by an adult. Children under 5, and children who cannot swim, must have an adult within arm's reach.
Life jackets and floats are not allowed in the deep part of the swim area.
There are restrooms, lockers, showers and changing rooms at the Visitor Services Center.

Open-water swimming outside the beach area is only allowed in organized groups — Boulder Aquatic Masters on Tuesday and Thursday mornings, and Stroke & Stride on Thursday evenings — and during triathlons.

Boating

Boats of every kind use the reservoir, from paddleboards and kayaks to sailboats and power boats, and the city lists water skiing as one of the activities. Every boat needs a current Boulder Reservoir watercraft permit. That includes paddleboards, kayaks, canoes, inflatable rafts, kite boards and windsurfers. No boat without a permit may enter.

Permits for small boats are sold online only, up to three per person. A boat inspector puts the permit sticker on your boat the first time you bring it. Jet skis, e-foils and jet boards are not allowed. Some hours on Tuesdays, Thursdays and Sundays are "no wake" or "limited wake," to keep the water calm for paddlers. Boat rentals are also available at the reservoir.

Walking, Running and Biking

The city's history page describes a mostly unpaved route of about 5 miles around the reservoir. Today, part of it is closed. Since Dec. 15, 2023, the west side of the reservoir has been closed all year to support the city's program to keep aquatic nuisance species out of the lake. Areas where osprey, American bittern, northern harrier and burrowing owl nest are also closed. The closures are marked on land and on the water. Going into a closed area can bring a court summons, with fines of up to $1,000.

Runners, walkers and cyclists pay a lower entry fee than people in cars (see below).

Wildlife

The reservoir is home to bass, catfish and walleye, and to osprey, hawks and other raptors, herons, owls, rabbits, snakes and prairie dogs. The city says the marshes and grasslands around the reservoir support more nests of Boulder County's birds of special concern than any other area of the same size in the county. Volunteers have watched those nests since 2004.

Fishing follows state rules, so you need a Colorado fishing license. Do not feed the wildlife.

Fees

The city charges a daily entry fee from April 1 to Oct. 31. Everyone who enters pays, including people on foot or on a bike. From Nov. 1 to March 31, entry is free.

From May 22 to Sept. 7 in 2026, the fees were:

$12 per person, age 3 and up
$20 for a car with two people
$30 for a car with three to five people, plus $5 for each extra person
$5 for walkers, runners and cyclists
After 6 p.m., $5 per person or $10 per car

In April, May and from September to October, entry was $5 per person or $10 per car. Season passes are also sold, with lower prices for Boulder residents.

Rules to Know

From the city's rules page:

No glass anywhere at the reservoir.
Dogs are not allowed inside the gates or on the south shore from May 15 through Labor Day. At other times, dogs must be on a leash.
No fires, and no charcoal or wood grills of your own. Propane grills are allowed with a fire extinguisher nearby; extinguishers and charcoal grills can be rented.
No smoking of any kind.
No camping, and no cars left inside the gate overnight.
Music and amplified sound only between 7 a.m. and 7 p.m.
Alcohol is allowed at private functions, but outside alcohol is not allowed on July 4.

Practical Information

Address: 5275 Reservoir Rd., Boulder, CO 80301
Swim season: Memorial Day weekend to Labor Day
Entry fees: April 1 to Oct. 31; free Nov. 1 to March 31
Food: The Lakeside@Boulder cafe is at the reservoir
Website: Boulder Reservoir, City of Boulder — for hours, events and email updates

Should You Go?

For people in 80304, the reservoir is the nearest big lake for a summer swim, a paddle or a long walk by the water. Go early on hot weekends. Check the swim area and fee pages before you go, and bring your boat permit if you plan to paddle.