Lay-bys near a beauty spot in the Brecon Beacons have had to be blocked off to stop people from having sex in their vehicles.
Welsh Water has had to install concrete blocks around the Llwyn Onn reservoir after they received numerous complaints about people dogging. The reservoir is just north of Merthyr Tydfil.
The parking restrictions have also affected people fishing as well as ramblers. Sandra Davies, of Merthyr Valley Ramblers, told the BBC that the move was "a bit too much".
Ms Davies told Vanessa Feltz, hosting BBC Radio 2's Jeremy Vine Show: "I do feel for the residents but these people have taken the enjoyment away from everyone else."
Ms Davies also added that all blocking these lay-bys would do is push doggers into other areas. She planned to raise her concerns with the Ramblers' UK head office.
A spokesman for Welsh Water said: "We're working to improve access points around the site for those on foot, so visitors genuinely using the reservoir and the facilities can continue to do so."
By Ted Welford