Three people in Surrey, B.C. have been hospitalized with Legionnaires' Disease, a severe form of pneumonia that develops after being infected by the Legionella bacteria.
They should also seek medical treatment if they've been in the Guildford area since August 21.
Most people don't get sick from exposure, but those with chronic health conditions, the elderly or smokers are more at risk.
Symptoms can include cough, fatigue, fever, abdominal pain, diarrhea, said Fraser Health Medical Health Officer Dr. Aamir Bharmal.
Anyone showing symptoms who was in Surrey's Guildford neighbourhood in the past 10 days should also inform their doctor, the health authority added.
The Department of Health found six of the 13 water tanks at the Saint Nicholas Houses tested positive for elevated levels of Legionella bacteria. It can also become aerosolized and be breathed in.
It can in extreme cases be fatal.
Legionnaires' disease is caused when people breathe in small droplets of water containing the bacterium known as Legionella, often found in freshwater, groundwater and soil, as well as cooling towers, hot tubs, and larger plumbing systems.
DHHS and the CDC will continue the investigation throughout the Labor Day weekend, including additional environmental testing and conducting interviews and re-interviews with the individuals who contracted the disease.