Fairlop Waters is a popular spot for watersports.

A schoolboy’s leg was “cut to the bone” by a boat propeller in Fairlop Waters, according to a witness.

The horrific accident happened on an end-of-term school trip at the Fairlop Waters Outdoor Activity Centre in Barkingside on Tuesday.

The 11-year-old, from St Mary’s Catholic Primary School in Chingford, was on a raft-building exercise on the lake when his shoelaces were reportedly caught in the propeller of a patrol boat.

A witness, who did not want to be named, said: “The blade cut into his calf, it was open about five inches all the way to the bone.

“He was a really brave lad. His colour went to grey and they gave him oxygen when he was in the water.”

Firefighters from Dagenham station happened to be across the lake on a training exercise and rushed to the boy’s aid in a boat.

Watch manager Lee Ware said: “We went in to release his leg. It was trapped by his shoelaces and we cut the laces and brought him to the shore.

“The injury was serious but not life-threatening.”

A London Ambulance Service spokesman said the boy was “conscious and breathing” when he was taken to hospital by air ambulance.

He was flown to the Major Trauma Unit of the Royal London Hospital in Whitechapel.

The boy is thought to be in a stable condition in hospital following an operation.

A statement on behalf of the school governing body said: “Our thoughts go out to the child’s parents.

“St Mary’s Catholic Primary School would like to thank the emergency services for their rapid response to the incident and the staff at Fairlop Waters.”

The activity centre is operated by Vision, which runs Redbridge Council’s leisure services.

A council spokesman said: “A full investigation is taking place, which is the normal procedure for such an incident.

“We would like to wish the boy a speedy recovery.”