Divemaster

General Feat (Prerequisite: Level 4+, Strength or Constitution 13+)

You gain the following benefits.

Ability Score Increase. Increase your Strength or Constitution score by 1, to a maximum of 20.

Swim Speed. You gain a Swim Speed equal to your Speed.

Free Diver. You can hold your breath for a number of minutes equal to 5 plus double your Constitution modifier (minimum of 5 minutes) 

Aquatic Athlete. While swimming you can take the Dash action as a bonus action.