Firefighters said chlorine spilled into the lazy river at a family sports fitness club owned by Mattress Mack just before 5 p.m. in the 1200 block of Wilcrest Drive.
Authorities initially said seven children and three adults were taken to the hospital after possibly ingesting chlorine. In an update, HFD said 12 people were hospitalized.
Chief Samuel Peña tweeted that the spill was under control at about 8:25 p.m., applauding firefighter crews for quickly assisting club members. He said an over-chlorination of the pool caused the incident.