Security has been increased at Grovebury Quarry because trespassers have been treating the site like a beach during the heatwave.
Quarry bosses are warning the public of the dangers of swimming in the lake at the site, which is situated on the southern side of the Leighton Buzzard bypass.
Aggregate Industries, which owns the sand quarry, has had to step up security in recent weeks because groups of people have been risking their lives by swimming at the site.
Tom Wise, General Manager at Grovebury Quarry, said: “Swimming at a lake within a working quarry is extremely dangerous. Trespassers are risking their lives and it’s not the first time this has happened.
“Six years ago, messages on social networking sites encouraged large groups to congregate here on more than one occasion, and there was evidence that groups of up to fifty or sixty people were here at any one time.
“Behaviour like this could result in a serious accident or death. The sand banks are likely to be unstable and could collapse at any time. Swimmers have no knowledge of how deep the water is or what lies beneath the surface and could drown, or even be buried alive. It’s that serious.”
The quarry has signposted warnings around the site, encouraging people to stick to the footpaths. They also have boundary fences in place, to stop people wandering onto the operational parts of the quarry.
These barriers are a legal requirement and security guards are in place to man the perimeter. However, increasingly, the security guards are having to stray from their main duties and instead redirect members of the public back to the nearest footpath.
Mr Wise added: “We understand that when the sun is shining, people want to get outside and enjoy everything the great outdoors has to offer. However, we’re asking that members of the public heed our advice and stay safe.”
Round the clock security patrols are now in place and Aggregate Industries says those caught trespassing on the quarry could face prosecution.