From Sonic Retro
The Propeller Shoes are essentially the aquatic variant of the Rocket Shoes in that they are a pair of sneakers with engines on them, and whereas the Rocket Shoes are found in various Zones, these shoes only appear in Tidal Plant Zone when playing as Sonic. When Sonic breaks open a monitor containing the shoes, he gains the ability to swim at high speeds underwater for eight seconds. During this time, the player can move Sonic in eight directions using the D-Pad. Should Sonic bump into anything hazardous, he will instantly lose the shoes.