https://worldbuilderblog.me/2016/07/14/common-potions/

Oil of Buoyancy

Potion Common

This murky oil reeks of the sea and can be poured over the body of one Medium or smaller creature. Applying the oil takes 1 minute. Once applied, the creature gains a swimming speed equal to its walking speed for 1 hour. During this time, the creature has advantage on Strength (Athletics) checks made to swim.