Roads near Windermere will be very congested this weekend as thousands of people attend the Great North Swim.
The event is getting bigger and bigger each year since it began in 2008.
From Friday to Sunday, 22,000 swimmers will take to England's largest lake for a half mile, one mile, two miles or 5km swim in open water.
They all have incredible stories for why they're doing it, whether it's for the love of the sport or as challenge to raise money for charities close to their hearts.
One year Blue-Green Algae cancelled the Great North Swim. Last weekend, traces of it were found but organisers say it's not enough to make the event dangerous and it's still going ahead.
Only a quarter of the athletes are from from North West England. East Anglia is the second most popular.
For some swimmers, it's taken a lot of hard work to be able to swim the distance. Open-water swimming has become much more popular in the last 10 years.