Several people were taken to the hospital on Monday after being exposed to high levels of chlorine while swimming in the pool of a west suburban hotel.

According to Elmhurst Fire Department battalion chief Mike Kopp quoted by the Chicago Tribune, the New Mayan Adventure water park in the Holiday Inn Chicago-Elmhurst at 624 N. York St. was crowded with dozens of children as schools were closed because of Martin Luther King Jr. Day.

About 22 people were taken to hospitals after showing signs of chemical burns around their eyes and mouth. According to witnesses, there were also children vomiting, coughing and bleeding from the nose or even fainting.

The incident took place around 1:15 p.m. and authorities suspect it was caused either by a chlorine leak or by a pool that was over treated with the chemical.

“We don’t know that exact cause- there’s more than one chemical used to regulate the pool,” said Ken Herman, general manager of the Holiday Inn Chicago-Elmhurst quoted by the Chicago Daily Herald.

Up to 18 ambulances were called to solve the situation and most of the people were transported to near hospitals. Six of them had symptoms that were more serious. Most of the victims were children.

Eleven people were taken to Elmhurst Memorial Hospital, one went to Alexian Brothers Medical Center in Elk Grove Village, four were taken to Loyola Medical Center, four patients were treated at the Adventist GlenOaks Hospital in Glendale Heights and the last two patients were taken to the Advocate Good Samaritan Hospital in Downers Grove. According to officials, all were expected to be released in the following days.

Until the health department will clear the cause of the incident, the water park will remain closed.