Staff at Coed y Brenin mountain bike centre in Wales are trying to trace vandals who attacked their trails.
Earlier this month, rangers discovered that rocks had been levered out of the ground on an old section of the Tawr trail, leaving large holes.
In addition, signs and way-markers had been broken and removed on the Dragon's Back and Beast trails – with some direction pointers changed to point riders in the wrong direction – and branches strewn across the track.
The damage, which affected several miles of trail, was discovered on a Friday afternoon, shortly before hordes of weekend visitors were set to descend on the popular centre, and staff had to act quickly to repair the vandalism.
Forestry Commission Wales mountain bike ranger Andy Braund said: "The waymarkers were tampered with on an extended loop in the furthest parts of the forest. They could have sent people out onto the moors, and the weather was pretty horrendous that weekend so we could have easily ended up with a man lost and going down with hypothermia.
"Rocks were removed from an old section of trail that used to be part of Tawr but no longer is – the old dual descender. It could have been a bit of high jinks but they don't realise the consequences. The damage to the trail was pretty bad. Anyone riding that section would have ended up going over the handlebars into the rocks. The potential for injury was high."
Rangers found evidence suggesting that motorbikes and quad bikes had used the trail shortly before the vandalism was discovered. They are appealing for information to help trace those responsible.
“It is unclear why anyone would want to cause damage and disruption on this scale," said Andy. "We've never had anything like this before. We are assisting the police in their inquiries in an effort to apprehend the culprits."