Officials are warning residents over the myriad dangers of cooling off with a dip in the River Thames this summer despite the ongoing heatwave.

With temperatures expected to hit 30 degrees Celcius on Tuesday (July 20) and Wednesday (July 21), the temptation to cool off in the nearby waters of London's famous river can seem irresistible at times.

Yet there are a number of pretty serious risks posed by swimming or even just dipping briefly in the Thames, the foremost of which is drowning.

In a video tweeted out by Richmond Council on Sunday (July 18), Lifeboat Operations Manager Matt Allchurch of the RNLI base in Teddington described just how dangerous the river can be.

"It's important to stress that you don't really know what you're jumping into when you jump from a footbridge (for example).

"There could be all sorts of obstructions under the water, there could be boats passing under you or other swimmers below you...

"The other danger is cold water shock. The body takes an involuntary breathe when you jump into cold water and that can result in two litres of water in your lungs which is instant drowning," he said.

"If you do survive that then the secondary measure of cold water shock is the loss of the ability to move your arms and legs because all your blood goes from your limbs to your core to protect your core.

"We have lost people in the last few years, young people, good swimmers, trying to swim across the Thames.

"Even in this warm weather we're having the Thames is still quite cold. We've had forty shouts this year already. All of them (with the exception of the whale) were people," he added.

Meanwhile, underwater currents can also present hazards to swimmers, by pulling them along or under the surface of the water and thus risking drowning or injury.

In addition to the dangers of drowning and cold water shock, there are less immediate, biological ones.

A Public Health England (PHE) report into the 2012 Hampton Court Swim between Hampton Court and Kingston Bridge found that a number of swimmers who took part had caught gastro-intestinal illnesses like Giardia as a result of the swim:

"Over 1,000 people took part in the swim and 338 reported experiencing symptoms of illness after the swim including nausea, diarrhoea, stomach cramps and vomiting," the study reported.

Recent reports showed that millions of tonnes of sewage are dumped into the Thames annually due to the river's outdated sewage control systems.