water scooter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A personal watercraft.
• noun A frame consisting of a narrow platform for the feet, a handlebar, and a hydrofoil, that is propelled by jumping up and pressing down.
• noun A hand-held, battery-operated device that spins a propeller to pull a swimmer through the water.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A recreational watercraft that the rider rides or stands on, rather than inside of, as in a boat.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a motorboat resembling a motor scooter