The public are being warned not to enter the water at Clatto Reservoir in Dundee after reports of boys jumping off a tower.
Locals claim the heatwave has tempted teenagers to use the sluice tower as a diving platform.
Environmental group Friends of Clatto reported its concerns to Dundee City Council – which led to the jetty being moved.
Secretary Dorothy McHugh said: “The boys were using the jetty to climb on to the tower.
“We felt this was particularly dangerous and were worried that when the boys dived they might land headfirst on the jetty.
“We can see it’s great fun for the boys doing this in this hot weather but we were very worried.
“I spoke to the boys, who were polite and just having a lot of fun.
“Friends of Clatto are happy to see the young people enjoying themselves in the sunshine.
“We just want them to stay safe, to be aware that the water at the sluice tower is 25ft deep, and to make sure there is a lifebelt nearby.
“The last thing we want is for an accident to happen or for anyone to get hurt.”
A Dundee City Council spokesman said: “Members of the public should not enter the water at Clatto Reservoir for the purposes of recreational swimming.
“Currently, there is signage at the location advising against entering the water for this purpose, with additional signage to be installed.”
The warning comes as Tayside is basking in temperatures of more than 25C.