Vandals have felled trees, started fires and left litter at a nature reserve which is home to a rare population of red squirrels.
The Havannah Nature Reserve in Newcastle has been "overused and abused" during the coronavirus lockdown, its protectors claim.
Firefighters were called out to the site five times in 48 hours earlier in the week.
The reserve, in Hazelrigg, is located at a disused colliery.
The Friends of Havannah group said: "Entire trees have been cut down, whilst others have been hacked into, to build dens and start fires.
"Beer bottles, crisp and biscuit packets - some still full - tin cans, barbecues, cutlery and condoms have all been left littering the reserve, as well as human faeces.
"This type of behaviour damages and destroys living organisms and harms the environment. And it's downright disgusting."
There are an estimated 140,000 red squirrels in the UK, but in England their populations are restricted to isolated parts of Northumberland, Cumbria and the south coast.
Urban Green Newcastle, which manages the land, said the incidents "could have put people and wildlife in danger".
Chief executive James Cross said there has also been an increase in littering across Newcastle since lockdown restrictions were eased, according to the Local Democracy Reporting Service.
He said patrols and litter picking have been increased and more temporary bins installed.
Mr Cross said: "We want people to be proud of their local park and look after it, especially at a time when we need our shared spaces the most."
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