Authorities say the pool where about 40 kindergarten students became ill will remain closed indefinitely until it's determined what happened.

The chief executive for North Central Health Care Center says excessive chlorine levels are suspected in Friday's incident but that remains uncertain.

Gary Bezucha says water testing immediately after the students got sick found normal concentrations and the investigation into what were described as acrid fumes continues.

The kindergartners from Lincoln Elementary School were at the center's therapeutic pool for water safety training when they began having difficulty breathing.

They were rushed to two area hospitals and most were treated and released. One boy remains hospitalized today in good condition at St. Joseph's Hospital in Marshfield.