How fast do dolphins swim?
You may have seen film of dolphins swimming alongside a fast boat and leaping as they go. Dolphins are streamlined and have evolved to slip through the water cleanly.
An efficient travelling speed for a dolphin is about 4-6 miles (6-9.5 kilometres) per hour.
Dolphin's fast 'cruising speed' is between about 8-10 miles (13-16 kilometres) per hour. They can keep going at that speed for some time.
Dolphins have been observed getting up to speeds of about 16 miles (or 26 kilometres) per hour over shorter distances of about a mile (1.6 kilometres).
If dolphins have a wave behind them, or the bow wave of a boat to carry them along, they might go much faster.
Dolphins might get up to about 17 miles (27 kilometres) per hour over very short distances, for example to do a big jump out of the water.
By contrast one of the world's fastest athletes Usain Bolt can reach about 23 miles (35 kilometres) per hour over 200 metres, but then he has to slow down again. A good marathon runner may run 12 miles (19 kilometres) per hour. Most people walk at about 3.5 miles (5.5 kilometres) per hour.
When dolphins want to go faster, they start jumping clear of the water, which is called 'porpoising' or 'breaching'.
It may look like dolphins showing off when they 'porpoise', but they're actually saving energy by jumping clear of the water, because air has less drag than water.
Why do dolphins chase alongside the bows of ships? The bow wave helps dolphins go faster with less energy, so if they're travelling in the same direction, it's like hitching a lift. They may well just do it for fun though.