A dozen people -- including seven children -- in Houston were taken to the hospital for chemical exposure due to an apparent over-chlorination of a lazy river pool, authorities said.

Houston fire officials received the initial call about the incident around 5 p.m. on Saturday, according to CNN affiliate KHOU.

Houston Fire Department Chief Samuel Peña tweeted Saturday evening that the incident was under control.

In an earlier tweet, the Houston Fire Department said seven children and three adults were transported to an area hospital, while others went by private vehicle.

KHOU reported that the conditions of those hospitalized were not known.

Chlorine is used in pools to eliminate germs. The chief noted that exposure to over-chlorination in such a setting can trigger nausea, skin and eye irritation or asthma symptoms.

The pool incident comes as residents are trying to stay cool amid high temperatures, with heat indices in the triple digits this weekend, according to the National Weather Service office in Houston.