The last step of the Turk's Challenge, in the Alter Ego mission, will ask you to catch a fish while wearing the Sailor outfit. The map is full of water points and small rivers where you can fish quietly and complete this challenge. Nothing difficult since you only need to wear the right outfit — which is automatically unlocked with the purchase of the Battle Pass.
There is only one subtlety to this challenge: you have to catch a "real fish". Even if Small Fry are technically fishes, fishing some will not validate your challenge. You'll have to catch a Flopper (Uncommon) instead.
