Authorities in Cold Spring, Minnesota, are investigating a chlorine leak at a high school swimming pool that sent 36 students and the gym teacher to the hospital.
The teacher and a dozen students have been admitted overnight for observation but a hospital spokeswoman says they were not seriously hurt.
The building was evacuated when the leak was discovered early Wednesday afternoon.
The school superintendent says students in the gym class saw bubbles coming out of the pool drain when the water was turned back on after some routine work in the chemical room. Soon after, they started feeling sick.