A downward-sucking, circular eddy in the sea, produced by a tidal current flowing through a tight, irregular underwater channel, or at the point where two or more strong currents meet in a river, is called a whirlpool. The effect is similar to the swirling action of waters circling and recircling in a basin at the foot of a major waterfall, such as the one at Niagara Falls, or to the turning of waters in a rocky gorge, as in the one downstream from Niagara. Whirlpools have occasionally been literary metaphors for disorder, famously in The Odyssey, where Homer personified a deadly whirlpool called Charybdis, caused by a formation of rock on the Italian side of the Strait of Messina, opposite a sea cliff on the Sicilian side, as a female sea monster given to devouring sailors.

William Kittredge