Whirlpool

A whirlpool is a body of rotating water produced by opposing currents or a current running into an obstacle.^{[1][clarification needed]} Small whirlpools form when a bath or a sink is draining. More powerful ones formed in seas or oceans may be called maelstroms (/ˈmeɪlstrɒm, -rəm/ MAYL-strom, -⁠strəm). Vortex is the proper term for a whirlpool that has a downdraft.^{[citation needed]}

In narrow ocean straits with fast flowing water, whirlpools are often caused by tides. Many stories tell of ships being sucked into a maelstrom, although only smaller craft are actually in danger.^[2] Smaller whirlpools appear at river rapids^[3] and can be observed downstream of artificial structures such as weirs and dams. Large cataracts, such as Niagara Falls, produce strong whirlpools.