Whale sharks can grow up to 12 metres long and weigh as much as 20 tonnes - heavier than three African elephants. Their mouths can be over a metre wide, but their throat is only the size of a tennis ball, so there is no chance of swallowing anything larger than a small fish. They are filter feeders, meaning they gather food by swimming forward with their mouths open and sieving water through hundreds of tiny filter pads.
Their skin is dark grey or blue-grey, covered with a beautiful pattern of pale spots and stripes that is unique to each individual - like a fingerprint. Researchers photograph the spot patterns of whale sharks and use computer software to recognise and track individual animals over many years.
South Ari Atoll in the Maldives is famous for having whale sharks year-round, making it one of the few places in the world where you can almost always find them. Scientists think the plankton-rich waters around Ari Atoll provide a reliable food source that keeps the sharks coming back.
Whale sharks swim slowly - about 5 kilometres per hour - and are generally not bothered by snorkellers swimming nearby. Meeting a whale shark in the water is described by many people as one of the most peaceful and awe-inspiring experiences in the ocean.