A woman from the USA has set a new world record by swimming four times non-stop across the English Channel.
Only four swimmers have swam three times in one go across the English Channel - that's the water between the UK and France - but no-one has ever completed a fourth leg.
Sarah Thomas began the epic challenge of more than 80 miles on Sunday and has completed her fourth and final leg. She finished the swim in 54 hours and ten minutes.
A group of celebrities are also going to try to swim across the English Channel.
The challenge is being documented in a TV series on Channel 4 called Sink or Swim, in which the stars will swim in relay from England to France in support of the charity Stand Up To Cancer.
Olympic gold medallist Greg Rutherford, Hollyoaks actress Rachel Adedeji and TV presenter Diane Louise Jordan are among those taking part.
But who was the first person to cross it? And what do you need to take on this epic challenge?
The English Channel is the stretch of water between England and France.
The shortest route to swim across it is 21 miles long, but that can change depending on the current.
The Channel is one of the busiest shipping lanes in the world, with 600 tankers and 200 ferries passing through it every day!
So you can't simply jump in and swim across. If you want to swim the 21 miles of the Channel, it has to be very carefully organised and planned.
The first recorded attempt to swim the Channel was in 1872 by a man called J B Johnson.
Not much is known about his experience, except that he was forced to stop after 1 hour and 3 minutes.
The first person to successfully cross the stretch of water was Captain Matthew Webb, who swam the distance in 1875.
It was his second attempt and it took him 21 hours and 45 minutes.
At the age of just 11 years and 336 days old, Tom Gregory became the youngest person ever to swim across the English Channel.
At 5am on 6 September 1988, Tom Gregory stood on the tip of France and set off for England.
In order to prepare, he didn't touch hot water from the Christmas before his attempt right up to getting in the water, taking cold showers and baths.
It took him 11 hours and 54 minutes.
No one younger has since completed the challenge - and no one ever will. In November 2000, the Channel Swimming Association banned under-16s from attempting the crossing.
In 2007, Bulgarian Peter Stoychev was the first swimmer to cross the channel in under seven hours, completing his crossing in an impressive 6 hours and 57 minutes.
But in 2012, his time was beaten by Trent Grimsey from Australia, who swam it two minutes faster.
Most swimmers assemble a team before they set off to help them to complete their challenge.
The team will typically include people who can provide medical assistance, moral support and a cup of tea!
They usually travel in a boat alongside the swimmer as they make their crossing.
Swimmers also often coat themselves in something slimy to avoid chaffing on the swim, which is why you might have seen photos of swimmers covered in goose fat.
Swimming the Channel is really popular, so those wanting to attempt the challenge often have to book it at least two years in advance.
Around 300 people take it on every single year, but only around one in five manage to complete it, so the swim is certainly not for the faint-hearted.
The most popular day to do it is 22 August. No fewer than 66 swims have been completed on that day over the years!