In many places, the rise or fall of the tide may create rotating currents in the waters. Some of these develop a downward thrust and are called maelstroms.

Naruto in Japan, is one of the world’s best known maelstroms. It occurs in the strait that links the inland lake of Seto with the Pacific Ocean. It is the third fastest maelstrom in the world, reaching speeds of up to 20 kph. Naruto’s vortices can reach diameters of up to 20 metres.

Moskstraumen – The Maelstrom – is found between the Lofotodden headland and the islands of Mosken and Værøy. It is also referred to simply as the Maelstrom.
The Maelstrom is 4-5 km wide and is considered one of the strongest of its kind in the world. The speed of the waters has been measured at 27.8 kph. The Maelstrom was described over 2000 years ago by the Greek historian Pytheas, and over the centuries it has been shown on innumerable sea charts accompanied by frightening illustrations and warnings. The Maelstrom is abundant in fish and has formed the basis of human settlement for thousands of years.

Old Sow between New Brunswick and Maine, USA.
Old Sow is considered the biggest maelstrom in the world, with some vortices reaching up to 75 metres in diameter. Moskstraumen, the Maelstrom, however, is a little faster.

Saltstraumen in Nordland is the world’s strongest tidal current.
It links the outer Saltenfjord to the Skjærstadfjord. Saltstraumen is 3 km long and is only 150 metres across at its narrowest. The speed of the current is about 40 kph. Boats can pass through Saltstraumen for about 2 hours after each ebb and flow. At lowest high tide greater masses of water pass through Saltstraumen than through Norway’s biggest rivers during times of flooding. In the course of about 6 hours, 372 million cubic metres of sea water are pressed through the narrow passage which is no more than 150 metres wide and 32 metres deep.