Swimmers await medical attention after the pool at the Cariboo Memorial Recreation Complex in Williams Lake was evacuated Sunday morning because of a chlorine incident. Swimmers await medical attention after the pool at the Cariboo Memorial Recreation Complex in Williams Lake was evacuated Sunday morning because of a chlorine incident. (Greg Fry)

Officials have determined a failed vacuum regulator caused the major chlorine leak at a Williams Lake, B.C., pool on Sunday.

The leak sent 70 people to hospital — including 45 children who were at the Cariboo Memorial Recreation Complex in Williams Lake for a swim meet.

Mayor Kerry Cook says a staff member was re-filling the wading pool, near the main pool, when chlorine was released. Swimmers reported seeing orange liquid in the pool before it was evacuated.

"The chlorine gas release was a result of a failed vacuum regulator which allowed chlorine gas to fill water delivery pipes and the filter system," said Cook on Friday.

Cook said an official, more detailed, report into the incident isn't expected for several more weeks.

Of the 70 people sent to hospital after the leak, two were admitted overnight: one adult and one child.

The adult was released by medical staff the next morning but Cook said the child, a young boy, was only released from hospital on Friday.

The pool remains closed and officials couldn't say when it would re-open.