You favor your aquatic elf parent and have developed the ability to breathe and move about in water easily.
Prerequisite: Aquatic half-elf.
Benefit: You can breathe water as well as air. Your swim speed improves to 20 feet.
Normal: Aquatic half-elves without this feat cannot breathe water and have a swim speed of 15 feet.
Source: Stormwrack, page 94.