Swim beach at Boulder Reservoir closed due to possible algae bloom

Officials have closed the swim beach at Boulder Reservoir after the city says a potential algae bloom was spotted Saturday morning.

City officials said they decided to temporarily close the beach out of an abundance of caution and asked visitors to keep their pets out of the water. The reservoir is still available for watercraft use, but officials warned that users should avoid contact with the water in areas that appear to have harmful algae blooms.

At high concentrations, blue-green algae, or cyanobacteria, can cause rashes, gastrointestinal issues, muscle weakness, or even vomiting. They can be particularly harmful to pets.

Those blooms can resemble thick pea soup or bluish-green paint spilled on the water's surface. They can also look like a thick mat of foam along the shoreline or short grass clippings.

Staff are collecting samples and will monitor algae bloom tests overnight; they said more information will be available on Sunday.

The city says the reservoir is used only periodically as a water source for the city and is not currently being used as a drinking water supply. Boulder officials added that they're working with Northern Water because the reservoir is used for irrigation and recreation.

According to the Colorado Department of Public Health and Environment's Toxic Algae Dashboard, there are currently caution notices or warnings at 8 bodies of water across the state. Of those, the algal blooms in Deweese Reservoir and Lake John are reportedly producing low levels of toxins.