Swimming Area and Beach

The Boulder Reservoir offers one of the largest seasonally lifeguard attended beaches in Colorado.

Swim Hours

The swim area is CLOSED for the season and will reopen on Friday, May 26, 2023.

Swimming is only permitted in the designated swim area while a lifeguard is on duty during established hours from 10am-6pm daily.

The current water temperature as of 11/3/2022 is 45 degrees.

Open Water Swim

Open water swimming at the Boulder Reservoir is available through Boulder Aquatic Masters (BAM) and Stroke and Stride. Otherwise, per city code, no swimming is allowed outside the designated lifeguarded swim area.

  • BAM - Finished for the season. Additional fees may apply.
  • Stroke & Stride - Finished for the season. Additional fees may apply.

General Information

This designated swimming area with rafts is the only location at the Boulder Reservoir where swimming is permitted, with the exception of lifeguarded open water swims and triathlons. Swim season is Memorial Day weekend through Labor Day.

Water temperature: The minimum water temperature to open the swim area is 60°F for the shallow area and 64°F for the entire swim area to open. The temperature fluctuates throughout the season. For the most up-to-date temperature, please call 303-441-3461, and then press '0' for the attendant.

Hours: Swimming is only permitted during established swim area hours. The swim area is generally open from 10 a.m. to 6 p.m., except Thursdays when the swim area closes at 5:30 p.m. for weekly Stroke & Stride events.

The swim area and beach may close at any time due to weather or for other health/safety concerns.

Lifeguards: The swimming area and beach is staffed by American Red Cross waterfront certified lifeguards during designated swimming hours only. Swimming is only allowed when lifeguards are present and on duty, and only in the designated swimming area.

Facilities: There are restrooms, lockers, shower and changing facilities located on the south side of the Visitor Services Center.

First Aid: The first aid station is located at the lifeguard shack. Please approach a lifeguard not on surveillance duty for assistance , unless it is an emergency.

Safety Rules

  • No swimming unless lifeguards are present and on duty.

  • No swimming anywhere outside the designated swim area.

  • Children under 13 must be supervised by an adult at all times. Children under 5 and/or non-swimming children must have an adult within arms reach at all times.

  • Personal flotation devices (PFDs) are not allowed in the deep swim area.

  • Inner tubes, body boards, and other flotation devices are not allowed in the deep swim area.

  • Test/Mark/Protect - Children under 13 must successfully complete a swim test and wear a wrist band to enter the deep area. Tests are offered by a head lifeguard at the middle lifeguard stand at the top of each hour, if business allows. Test may be attempted once per day, and are valid for the duration of the season.

  • Diving is not allowed anywhere, including off rafts.

  • Any holes dug in the sand must be filled.

  • Alcohol is not permitted in the deep swim area.

  • Glass is prohibited in the entire park.


Weather at the Boulder Reservoir is unpredictable and can change rapidly, becoming dangerous to boaters, swimmers, and other visitors. Be aware of rapid cloud build-up, drop in temperature and sudden changes in wind direction or speed as these may signal the arrival of dangerous weather conditions. A link to the weather monitoring station will be posted here when available.

  • THUNDER/LIGHTNING: When lightning is seen or thunder is heard near the Reservoir, the swim area and beach will close for 30 minutes from the last lightning seen or thunder heard. It is strongly recommended that people take immediate shelter in their cars. It is not safe to take shelter under a tent, tree or building, or anywhere within 100 feet of the shore when lightning is present.
  • WIND: When wind is high enough to create rough water that decreases visibility, the swim area will close.
  • FOG: When fog is thick enough to decrease visibility, the swim area will close.

Weather Warning Flags: A flag is displayed at the lifeguard shack to indicate existing or imminent weather conditions, which are or may become dangerous.

  • Green: Low Hazard. Calm conditions.
  • Orange: Medium Hazard. Moderate weather conditions including rain, wind, or rough water that may decrease visibility for lifeguards . Exercise caution.
  • Red: High Hazard. Swim area and beach closed to users.
  • Purple: Environmental Hazard. Swim area is closed to users.


If you are bringing a group of 10 or more, we ask that you make a reservation at least two weeks in advance. A swim reservation does not guarantee or reserve space or amenities; it simply provides us with a heads up to ensure adequate lifeguard staffing. Large groups without a swim reservation may be turned away.