Last updated at 10:04am on 18.06.08
Would-be revellers are using satellite images on the internet to find houses with swimming pools - and then turning up uninvited for an impromptu dip.
The craze involves using the Google Earth programme, which provides high-quality aerial photos of Britain and other countries.
Once a target is chosen, the organisers use social networking sites such as Facebook and Bebo to arrange to meet, say police.
Officers said that residents have woken up to find youngsters 'dipping' in their back gardens, or have come home from work to a swimming pool full of beer cans.
One group has already boasted on the internet that it held an event earlier this week.
Sixteen people are said to have gatecrashed two pools near Bournemouth.
The rules of 'dipping' often include wearing fancy dress and participants are urged to 'bring a bike' to escape if discovered.
There are fears that the craze could spread across the UK as the weather improves and pool owners leave their homes unattended while on holiday.
A spokesman for Devon and Cornwall Police said yesterday: 'We are advising owners of swimming pools to be on their guard.
'We would also warn prospective swimmers that using someone else's pool is trespassing and therefore illegal.'