A whirlpool is a rotary current in water. Permanent whilpools may arise in the ocean from the interaction of tides. The occur also in streams or rivers where two currents meet or the shape of the channel dictates. Short-lived whirlpools may be created by wind.

Very powerful whilpools are called maelstroms. The original one of these, described in fiction by Edgar Allen Poe and others, is the Moskstraumen, a powerful tidal current in the Lofoten Islands off the Norwegian coast.