Illegal campers have turned part of Kielder Water and Forest Park into a "mess".
Pictures, posted on Facebook, show tents, chairs and rubbish abandoned at the North East beauty spot.
Police have now issued a warning while the park has prohibited wild camping there for the rest of the year.
"Sadly due to continued illegal camping taking place (thankfully this is reducing slightly) and items being left behind for our staff to gather up, damage to habits etc we are unable for the remainder of 2020 to allow any form of wild camping," posted the park on Facebook.
"This includes the limited locations with permission where backpackers have enjoyed a night under stars in remote locations.
"In the last fortnight we again have had to deal with illegal camps as in the photo below of a major camp left with much mess - details of specific information is now with Northumbria Police and being followed up.
"We do want people to enjoy camping at Kielder and we are delighted that Kielder Campsite is open again so this can happen in a controlled way."
Campers will now have to book and show identification if they wish to camp, which costs £10-a-night.
Neighbourhood Sergeant Kate Benson, of Northumbria Police, said: "We are aware of concerns from the Forestry Commission about illegal camping at Kielder and have been working closely with them to address the issue.
"We have stepped up patrols in the area and if we find anyone camping illegally then they will be moved on.
"Kielder is an incredibly beautiful place that is enjoyed by residents and tourists throughout the year and deserves to be shown a bit of respect.
"It is not acceptable for individuals to behave in this way, destroying the environment and leaving rubbish littered throughout the forest. We are committed to working with both the Forestry Commission and the local authority to clampdown on this kind of activity so we can preserve the local environment."
The park is a popular tourist attraction, and home to both the biggest man-made lake in Northern Europe and England's largest working forest.
