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Lifeboat crews were called to two skinny dippers trying to cool off with a late night swim in the Thames.

The pair were overheard saying they were "mermaids" after being found swimming near Deptford on the hottest night of the year so far.

After police arrive on the scene near Borthwick Wharf by boat at around 3.30am today, the man and the woman were seen running away into some nearby bushes.

One of the swimmers then emerged unhurt a short while later and was given a dressing down by an RNLI crew.

The Metropolitan Police's @MPSonthewater Twitter account posted after the incident: "2 naked persons located after a search with @TowerRNLI. Hot weather, alcohol and river swimming. Overheard saying they were mermaids #badidea".

The incident triggered a warning to Londoners from lifeboat crews about the dangers of swimming in the Thames, which is affected by notoriously strong currents.

Kevin Maynard, Tower RNLI lifeboat station manager, said: "London may be gripped by a heatwave but swimming in the River Thames is incredibly dangerous and we would strongly advise people not to do so. These two skinny dippers were lucky to escape unhurt as they had put themselves in a potentially life or death situation.

"The River Thames in London has very strong currents that can easily sweep you away. Combine this with the high number of obstacles in the river and swimmers can all too easily find themselves dragged under the water.

"There is also the danger of cold water shock. Despite the hot weather, the river water is still very cold and sudden exposure can cause uncontrollable gasping for air which leads to you gulping down water causing a real risk of drowning.

"If you’re suffering from the heat there are better and much safer ways to cool down than putting your life at risk by swimming in the River Thames."