People and their pets are being advised to steer clear of the water in Brunner Reservoir in Broomfield.
Broomfield Public Health and Environment on Thursday issued a warning that the reservoir, east of the Broomfield Community Center, has been experiencing a blue-green algae bloom.
A chemical produced by blue-green algae — Microcystin — can cause health problems in people and pets, either from skin exposure or ingestion.
Those at greater risk include children, toddlers, and pets who explore the shoreline or play in the water, according to the city.
When the concentration of Microcystin is high enough (greater than 20 parts per billion, also known as the "action limit"), it can irritate eyes and skin that come in contact with water. If ingested, it can irritate the esophagus and digestive tract.
The risks to humans and pets come from prolonged contact with skin and from swallowing the water.
Symptoms from external exposure are skin rashes, lesions and blisters. More severe cases can include mouth ulcers, ulcers inside the nose, eye and/or ear irritation and blistering of the lips, according to a news release issued by the city.
Symptoms from ingestion can include headaches, nausea, muscular pains, central abdominal pain, diarrhea and vomiting. Severe cases could include seizures, liver failure, respiratory arrest, and even death, although this is rare, the release stated. The severity of the illness is related to the amount of water ingested and the concentrations of the toxins, according to the release.
Currently, there is not a method or chemical to "treat" the pond for the blue-green algae other than aeration, which limits algae growth, according to the city.
Signs have been posted around the reservoir and Public Health staff recommends people and pets avoid all contact with the water until the warning signs are removed.
"We have experienced outbreaks of this algae in other ponds and have handled the situation on this same manner. We do not believe this outbreak is connected to last week's rains," City and County Manager Charles Ozaki stated in the release.
The reservoir will continue to be monitored until the algae bloom dies off and levels are below the Microcystin action limit, the release stated.