A vortex that forms at sea where currents from different directions interact, often with a large obstruction on the seabed to set the water turning. Whirlpools usually form in narrow straits with strong tidal flows. They can be dangerous to small boats, mainly because of the large waves they generate. The world’s strongest whirlpools are Saltstraumen and Moskstraumen in Norway, and Corryvreckan, Scotland.