Perth’s drinking water is being put at risk with a spike in people camping, dirt biking and cutting and burning trees in a main catchment are in the hills, officials warn.

Department of Water and Environmental Regulation and Water Corporation director of water Susan Worley said there has been a “significant increase” in the number of people accessing the Mundaring Weir Catchment.

Footage of young children learning to ride dirt bikes on the same tracks as larger vehicles in the area was alarming, she said.

“The area is not safe for children to be riding and the department is concerned that if these unauthorised activities continue there is an increased risk of someone being seriously injured,” Ms Worley said.

“These activities are also placing the quality of our drinking water at risk.”

The land is part of a catchment that supplies water to Perth, the Goldfields and many town in-between.

The problem spots are around Flynn Rd, near the lakes and land at Wellbucket off Gorrie Road where officers have found signs of chainsaw use, arson, off-road use and camping.

The DWER and Forest Products Commission are currently undertaking plantation and landscape rehabilitation works on the area.

“This is a serious public safety issue,” Ms Worley said.

“You cannot have these kinds of unauthorised activities occurring in the same area as plantation and rehabilitation work.”

DWER officers said they are working closely with WA Police and the Water Corporation to monitor the issue.

Plans to increase no trespassing signage were placed at the site last weekend and DWER staff released information about appropriate activities to comply with in the area.

Surveillance will continue in the area, along with site visits.