pf2e.fyi
From Pathfinder Lost Omens Hellfire Dispatches, which isn't enabled.

Trained Swimmer

FEAT 4
ARCHETYPE
Archetype Undersea Privateer
Prerequisites Undersea Privateer Dedication

Thanks to tireless practice, water has become a natural environment for you. You gain a swim Speed of 15 feet. If you already have a permanent swim Speed, swimming up or down isn't difficult terrain.

Pathfinder Lost Omens Hellfire DispatchesORC