Tidal whirlpools are commonly found in oceans and seas, and are currents that move in a rotating direction. They are often caused by rising and falling tides that interact with each other. They also occur when currents flowing in opposite directions meet each other, causing friction. Friction will cause the water to spin, and this is common in tight areas with strong currents. Whirlpools in rivers often form because of the tight spaces and fast flowing water crashing into slower currents.
Waterfalls can produce whirlpools. In Niagara Falls, water rushing from the falls is forced into the gorge below it. The falling water disturbs the water below and will clash with different currents. The pressure of the falling water meets with the other currents causing swirling water, which eventually leads to whirlpools. Miniature whirlpools also form in sinks or bathtubs. These form when all of the water tries to flow down the drain at the same time, and the air from the drain pushes against the water causing it to spin. These small whirlpools do not form like whirlpools in nature do.
Many naturally occurring whirlpools exist all over the world, with the bigger, faster and stronger whirlpools becoming famous destinations for travelers. Two of the most famous whirlpools are Old Sow between New Brunswick and Maine and the Naruto whirlpools of Japan. Norway is home to two of the most powerful whirlpools, the Moskstraumen off the Loften Islands of Norway, and Saltstraumen, which is near Bodo. Canada, Scotland, Italy and Niagara Falls are also home to large and famous whirlpools.
All whirlpools vary in size and speed, with the most powerful whirlpools located in narrow straights that have fast currents. The Saltstraumen whirlpool in Norway produces the fastest current, reaching swirling water speeds of 25 mph, but other whirlpools in Scotland and Norway often come near the 20 mph mark. Whirlpools can be dangerous to small boats and people in the water near whirlpools. The currents move fast and can drown someone or bash a small boat into rocks. Large ships will often find whirlpool currents too hard to steer in. So while the exaggerated tales of large ships and crews being sucked into a whirlpool is untrue, whirlpools showcase a ton of natural power.