“Incredibly dangerous” booby traps have been found on popular cycle paths in the Peak District.
Items found in recent weeks include large rocks moved out of position, pins dropped on the road and branches arranged at head height across paths.
Chris Maloney, who runs a local cycling information blog, said while cyclists appeared to be the target, the obstacles could harm anyone.
Police said they had been made aware and appealed for information.
The traps have been spotted on trails and roads in Bradwell, Bamford and Aston, near the Derbyshire/South Yorkshire border. There are no reports of anyone being injured.
Blogger Chris Maloney, a member of mountain biking advocacy group Peak District MTB, said: “The worrying thing is we don’t know who it is who’s doing this kind of stuff.
“It’s somebody with a vendetta, someone who has something against we assume mountain bikers or riders – but the things they’re putting out do not discriminate.
“It’s an incredibly dangerous and reckless thing to do.”
Derbyshire Police said no official complaints had been made but said there have been previous incidents where tacks were placed on roads in and around some villages.
“Anyone acting in this manner is putting people at serious risk of injury and, potentially, even death. It is not just cyclists that could be affected – horses and their riders, walkers and other trail users could all be hurt,” the force said.
South Yorkshire Police said it was also aware of reports of alleged trail sabotaging.
Traps have also been found at mountain biking trails elsewhere in the UK, including a plank of wood with 200 nails embedded in it, found in a forest path in Wales.