This challenge is part of the 8-Ball vs Scratch Mission that closes the first season of Fortnite Chapter 2. You'll haveto swim not far from two different "No Swimming" signs. It's a simple challenge with only one condition: to know where the signs are located.
Map
North of Misty Meadows
The first sign is located on the shores of the large lake above Misty Meadows. It is very precisely at the gates of the big dam.
South Island
The second sign is located next to the pontoon, on the small island at the extreme south of Apollo. It's a remarkable and relatively quiet place, you will in principle have no trouble to enjoy a little well-deserved swim.
We recommend the Team Rumble mode to achieve this challenge, especially during the week following its release. It'll reduce your chances of running into warring enemies as soon as you land.