A recent sighting of a potentially harmful algae bloom, also known as cyanobacteria, has prompted Boulder City officials to warn residents and visitors to steer clear of the Boulder Reservoir's waters. This precautionary measure was triggered after both city staff and community members reported the suspicious bloom in the area. Exposure to toxins produced by cyanobacteria at high levels can be detrimental to human and pet health, leading authorities to advise against swimming and allowing dogs in the water, as detailed by the City of Boulder.

The reservoir's swim beach is already closed for the season, however, watercraft are still permitted to operate. In light of the current algae situation, the city recommends watercraft users to avoid areas with active blooms, and overall, maintain a distance from the water to prevent any contact. While the blooms may vary in appearance, ranging from thick pea soup to a spilled paint-like substance or foamy shoreline mat, the warnings remain in place.

Although Boulder Reservoir currently does not serve as a source for the city's drinking water, the potential impact is still felt downstream as the Northern Colorado Water Conservancy District utilizes the reservoir for delivering water. Boulder officials are collaborating with Northern Water in managing the response to the cyanobacteria bloom situation. Simultaneously, city staff are diligently collecting water samples to ascertain the presence and concentrations of cyanotoxins in the reservoir's waters.

Till confirmation from the water testing results are available, the City of Boulder is urging residents to keep their dogs away from the reservoir and to avoid engaging in water-related recreational activities as a cautious approach. Indications of the harmful algae include exhibits such as a thick pea soup consistency or bluish-green discolorations on the water's surface which should serve as a sign for residents to keep at bay, the city's guidance notes.