Fins of Swimming (3.5e Equipment)
From D&D Wiki
This item resembles a pair of fins that can be attached to boots, rather similar in that fashion to crampons of climbing. When worn, they bestow upon the user a competence bonus to Swim checks equal to the fins' enhancement bonus.
Prereqs: Craft Wondrous Item, alter self. Caster level must be at least equal to the fins' enhancement bonus.
Cost to Create: 800 gp (+2), 3,200 gp (+4), 7,200 gp (+6), 12,800 gp (+8), 20,000 gp (+10).