Amulet of Buoyancy

This well-worn necklace is adorned with the bow of a ship and a crashing wave of blue glass. While wearing this amulet, you can use your reaction to immediately stand up when you're knocked prone. When you do, your speed is halved until the end of your next turn. In addition, if you start your turn underwater with 0 hit points, you immediately rise 60 feet toward the surface.