We may be basking in a heatwave but police are warning people about the dangers of swimming in open water.

Temperatures have soared set above 30 degrees today (Friday), with warm weather expected too over the weekend, and while it may be tempting to cool off by taking a dip, police are asking people to think twice.

Officers in Rickmansworth say they have seen a recent rise in reports of people swimming in the River Colne off Uxbridge Road, near to the weir while they have also warned about swimming at the Aquadrome.

Three Rivers Detective Inspector Stewart Moulding said: "Not only is open water swimming prohibited in some bodies of water such as Rickmansworth Aquadrome, it also comes with some very real risks for the inexperienced and we are asking the public to refrain from swimming in rivers, canals and lakes this weekend.

"It is almost impossible to determine the dangers that lie beneath the surface; you could become entangled in weeds or rubbish, contract a waterborne disease or be overpowered by a strong undercurrent.

"Please, it’s not worth the risk. We really do not want to be knocking on your loved one’s door to give them devastating news about what would be an entirely preventable tragedy."

The following advice about staying safe in a heatwave is from Hertfordshire Fire and Rescue Service:

• Even on a very hot day, the water can be freezing. As soon as you enter the water you can lose your breath and experience what is called cold water shock. It makes it hard for you to swim and can lead to drowning.

• There are many unseen dangers when swimming in a river, lake or canal. You can never know what dangers lie beneath the surface of open water, so it's better to wait for swimming pools to be open, or investigate whether local groups in your area run guided open water swimming.

• If you come across a water emergency, dial 999 straight away. Don’t attempt to get in to the water yourself to rescue someone – the chances are that you’ll need to be rescued too.

• Know your location so you can tell emergency services where you are. A great way to do this is to download the what3words app, which divides the world into 3 metre squares giving each location a unique address which will help 999 call handlers pinpoint your exact location in the event of an emergency. Search for it in your app store or visit what3words.com.