When you have a really powerful whirlpool, it's called a "maelstrom." Saltstraumen is the strongest maelstrom in the world. It is located off the coast of Norway near the Arctic Circle. The Saltstraumen forms four times a day as the tides carry large amounts of water through a small channel only 490 feet (150 meters) wide. The currents reach speeds of 25 miles per hour (40 kilometers per hour). When ships must pass through the area, they do so during the short windows of time in which the maelstrom is not active. Thousands of tourists visit the city of Bodø to view the maelstrom at high tide, when it is the strongest.