Twelve people, including seven children, were taken to the hospital for chemical exposure due to overchlorination of a lazy river in Houston, Texas.

Houston fire officials received the initial call about the incident around 5 p.m. on June 24 at the Club Westside fitness center.

According to the Houston Fire Department, the chemical exposure was caused by “a chlorine spill with possible accidental ingestion” in the lazy river.

Chief Samuel Peña tweeted that the spill was under control at about 8:25 p.m., about three and a half hours after the incident occurred, and applauded firefighter crews for quickly assisting club members.

Officials did not comment on the conditions of the people who were exposed.