In July 2017, Hennepin County Public Health (HCPH) staff investigated an outbreak of chemical poisoning among staff at an indoor waterpark at a hotel in Maple Grove, Minnesota. Six cases were identified. Symptoms included coughing, burning in their throat/lungs, nausea, difficulty breathing, headaches, dizziness, eye issues, running nose, gagging and sweating. The median incubation was 10 minutes (range, 0 to 110 minutes) after exposure to the waterpark on July 29. One case was hospitalized briefly and released.

Upon inspection of the waterpark by HCPH sanitarians on July 31, it was reported that shortly after 7:00 am on July 29, a strong chlorine smell was noted in the pool area. An HCPH sanitarian interviewed the chief pool engineer. It was reported that the night before the incident, the pool operator noticed that the oxidation-reduction potential was low and added an unknown amount of chlorine after the waterpark closed. The operator could not recall how much chlorine he added and did not document the amount. There was also a question of whether he added calcium hypochlorite or sodium hypochlorite.