A little bit north of the Arctic Circle in Norway is the world's most powerful tidal current called the Saltstraumen Maelstrom.
The current owes its existence to the gravitational pull of the sun and moon and the topography of Norway's mountains and fjords. A topography the locals call lovely crinkly edges.
The tides at this location rise and fall twice a day by about 2 m which is about 6 foot. As the water tries to maintain equal levels in the ocean and in the fjord it is forced through a narrow rocky passage, and that creates the strongest title current on earth.