The Carding Mill Valley, at Church Stretton, is open to visitors from dawn to dusk.
But those who live there say that the reservoir and valley are being used as a location to drink, party and socialise after hours when the National Trust has stopped manning the gates.
They say the litter problem is appalling and broken glass poses a threat to local wildlife, while, when facilities are closed the area is used as an open toilet.
Loud music continues well into the evening and night and there is often evidence of alcohol and drug abuse, they say.
Residents are also worried that the fires and barbeques will lead to a blaze on the Long Mynd and that an animal or a person will be seriously injured or killed because of the bad driving.
They have written an open letter to the National Trust and local authorities pleading for action to deal with the anti-social behaviour, including making alcohol free zones.
Resident and a landlord in the Carding Mill Valley, Tim Goldfield, said that, as well as evidence of drug abuse, alcohol usage at the reservoir had reached record levels.
He said the human excrement around the reservoir was a public health hazard.
"It is disgusting for local walkers and other users of the valley," Mr Goldfield said.
"It is only a matter of time until a serious fire is started on The Mynd, the fire risk made worse by the littering issue, with glass bottles constantly thrown in to the bushes just waiting to catch the sun and spark a fire."
The open letter says once the Trust staff leave, there is a noticeable increase in speeding and cruising up and down the valley.
"The road is supposed to 20mph, 10mph in places, but we often see cars going at full speed up and down the narrow road," it says.
"It is only a matter of time until someone is injured or an animal is killed. Most residents of the valley have stories of being abused by visitors if they challenge anti-social behaviour. "
Residents would like the National Trust, Shropshire Council and the police to work with them to help curtail the anti-social behaviour. They also want to see the reservoir and surrounding area made an Alcohol Free Zone.
Mr Goldfield said: "The Trust does not see the speeding and parking on verging as their issue as the road is a public highway and the land is common land. Whatever solution is proposed should not impact the use of the area by respectful visitors and locals who frequent the reservoir at all times of the year – not just hot days.
"Most visitors and locals do not use the reservoir as a place to drink or party but rather a place to walk, picnic and free swim. Prohibiting the consumption of alcohol would therefore generally not impact these users. Prohibiting alcohol would have an impact on a number of the points raised above whilst not impacting respectful use of the valley and reservoir. It would make it less attractive to visitors who only see the reservoir as a place to party. It would reduce the problems of littering and toileting and would also, hopefully, reduce the problems of people returning drunk late to their cars in the evening and making noise."
The open letter calls for a public space protection order for the area.
"We would like the council to work with us to provide better signage to help visitors understand the residential nature of the valley," Mr Goldfield added.
"Most visitors believe that the Trust owns all the buildings and this sometimes leads to a mistaken belief that the entire valley is an attraction they have paid to use as they wish."
A National Trust spokesperson said: “It is important that everyone has access to green spaces and an opportunity to connect with nature. The vast majority of visitors to Carding Mill Valley are very respectful and care for this special place as much as we do.
"Unfortunately, a minority have been causing some problems and we understand and share the concerns of local residents.
"We work closely with the council and the police and have taken several steps ourselves to mitigate the situation including recruiting additional staff, staff staying late during busy times, leaving toilets open into the evening and mobilising staff and volunteer teams to remove litter and rubbish quickly.
"We have been encouraged by the many positive comments we’ve received from Carding Mill Valley residents who understand the challenges and have said how well the team are managing.”