Britons looking to cool off during the extreme hot weather have been warned not to swim in a Somerset lake after high levels of E.coli were found.
Authorities have advised people to not swim in Clevedon Marine Lake, where bacteria levels are said to have tripled.
Tests showed that in the space of just one week, Enterococci bacteria levels had increased by 69 per cent.
Examinations found 'decreased' water quality, with heightened levels of the bacteria.
Traces of E.coli - which can cause vomiting and diarrhoea - were found in the lake, which is due to be drained a refilled.
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On Thursday morning, at 5.27am the official Clevedon Marine Lake Twitter account warned swimmers as temperatures nationwide began to heat up.
It read: “Latest tests show the water quality has decreased. Swimming is NOT ADVISED until further notice. The Lake will be DRAINED on 31st July.”
MARLENS was forced to drain the lake 10 months ago after traces of E.coli were found in the water.
In that instance, successful refilling saw water quality improve.
A yellow weather warning is in force for most of England, except the south-west, and parts of Scotland from 3pm on Thursday until 4am on Friday.
The Met Office predicts a 60 percent chance the current record of 38.5C could be broken.
"It will get into the 30s across the country and reach the mid-30s in the south-east," Met Office meteorologist Greg Dewhurst said.
However, the July record was broken at London Heathrow airport on Thursday, recording a staggering 36.9C.
It is even possible the mercury could climb to 40C, which would be “unprecedented” for the UK climate.