Police are appealing for witnesses after wooden pallets were set on fire in a nature reserve.
The incident happened at Joe's Pond in Redburn Row, Chilton Moor, on 10.45pm and 11pm on Monday, May 16.
Wooden pallets that were stacked at the side of a storage container, were set alight and burnt through.
A police spokesman said: "This damaged the storage container and its contents. It is believed the fire was started deliberately and it is being treated as arson.
"Officers are carrying out enquiries and appealing for any witnesses. It's believed three people were responsible for the fire and officers are keen to trace them, anyone who saw three people in the area should contact police."
Anyone with information is asked to contact Northumbria Police on 101 quoting reference 1310 160516 or Crimestoppers anonymously on 0800 555 111.