pf2e.fyi
From Pathfinder Lost Omens Impossible Lands, which isn't enabled.

Serpentine Swimmer

FEAT 9
Prerequisites Water Nagaji

You undulate your body in a series of sinuous serpentine motions as you swim, drastically improving the speed at which you move through the water. Your swim Speed increases from 10 feet to 25 feet.

Pathfinder Lost Omens Impossible LandsOGL