Mountain bikers who frequent the Don Valley trails have raised the alarm after a narrow wooden bridge on a ravine trail was sabotaged.

“Never cross any structure unless you’re sure of its safety,” Timothy Charles, founder of the Toronto Off-Road Biking Association, said yesterday.

He said the supporting beam of the bridge appears to have been deliberately cut partway through in several places that couldn’t be seen by anyone crossing above.

The damage put the structure at risk of collapsing, which could have caused serious neck injury, broken bones or worse, he said.

The bridge is one of several spanning gullies on the hillside of the ravine near Overlea Boulevard and Thorncliffe Park Drive.

The incident has sparked concern in the tight mountain biking community.