Malmesbury River Valleys Trust says it was disappointed to see bottles, nitrous oxide canisters and even a sofa right next to the sett entrance in their Conygre Mead park, off Mill Lane.
The trust also believes people, possibly groups of teenagers, have been starting campfires in the reserve, which could also harm the local wildlife and is a hazard in the drier months because of the bushes and shrubbery in the park.
Frances Goldstone, chairman of the charity, said volunteers are having to work even harder to clean up after others.
“We’ve had it up to our eyeballs with people who don’t respect the nature reserve,” she said.
“We’re constantly cleaning up litter. People are setting fires around the area. I just wish people would have more respect for the nature around us.
“We welcome the public to visit the reserve but it’s just being abused. We’ve found a lot of drug canisters left behind as well. We’re starting to feel betrayed by the small number of people who are starting to ruin it.
“We’re trying to create a place where nature is able to thrive and some people are making that difficult for us.
“The general disturbance these people are causing could really harm the wildlife around. Broken glass from bottles could hurt the animals.
“Thankfully the people who left the sofa collected it afterwards. They said they didn’t realise they weren’t allowed there but we have put up plenty of signs around the reserve that tell people they can’t leave things.”
The trust said they have also seen a number of people using the car park without paying and are soon to install a barrier to stop this from continuing.
Wiltshire Police have been made aware of anti-social behaviour in recent weeks and have sent out patrols to keep an eye on the situation.
The police have also said waste has been repeatedly dumped on the Fosse Way near Long Newnton.
Badgers are protected by law under the Wildlife and Countryside Act meaning that anyone caught killing or harming a badger, or interfering with a badger sett, can be prosecuted, with offenders facing a six month jail sentence and an unlimited fine.
Conygre Mead nature reserve, which is almost the size of five football pitches, is owned by the trust who bought the land for £25,000 in 1992 and homes hundreds of species of wildlife.