tidal current in the world. Up to 400 million m³ (tonnes) of  seawater  forces its way through a 3-kilometre (1.9 mi) long and 150-metre (490 ft) wide  strait  every six hours, with water speeds reaching 22  knots  (41  km/h ; 25  mph ).  Vortices  known as  whirlpools  or  maelstroms  up to 10 metres