Swimming determines if a character floats or sinks in water, as well as how fast he can move within it. A character's Pace is half his Swimming skill in inches per turn in normal water (round up). Choppy water counts as rough terrain and halves this rate. Characters may not “run” while swimming for extra movement.

Holding Your Breath: Characters can hold their breath for a number of rounds equal to 2 plus their Vigor die, or half that if they weren’t prepared for being submerged and didn't have time to get a good breath.

Drowning: The rules for drowning are found on page 100.

Savage Worlds Deluxe Edition p. 28