It’s larger than Japan, more than 1km deep and borders 5 countries – and is home to a unique seal population

There are millions of lakes across the world – with some estimates reaching up to the three million mark.

But what’s the world’s largest lake? The answer, it turns out, is somewhat confusing. Firstly, because the largest lake on the planet is actually called a sea. And secondly, it’s salty. For these reasons, it’s also referred to as the ‘world’s largest inland body of water’.

However, it is widely classified as a lake as it’s landlocked and connected to the ocean via rivers.

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What’s the biggest lake in the world?

You might think that the world’s biggest lake is in the Americas or Africa – but it’s actually in Eurasia. And, rather confusingly, it’s called the Caspian Sea.

The landlocked lake borders Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan. The Caucasus Mountains lie to its east, with the vast steppe of Central Asia to its west.

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The Caspian Sea spans an area of 149,200 square miles (386,400 square kilometres) – making it larger than the area of Japan (which is 145,946 square miles, or 378,000 square kilometres).

Its deepest point is 1,025 metres (3,360 feet) below the sea’s surface and the lake is thought to contain around one third of Earth’s inland surface water.

The Caspian Sea also holds the record for the largest salt lake on Earth.

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It contains 50 islands and is an important site for biodiversity. It’s home to the Caspian seal and six species of sturgeon, as well as hundreds of species of fish and invertebrates.

Scientists have tried to explain how the seal population got to the landlocked body of water, with the latest research suggesting that they travelled through a network of rivers from the Arctic north that have since disappeared.

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Plenty of birds migrating between Europe, Asia and Africa can also be found at the Caspian Sea.

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However, recent research has warned that the lake could shrink due to global warming. Scientists from Leeds University have predicted that an area larger than Iceland could evaporate by 2100.

The second largest lake in the world is Lake Superior, which is bordered by Canada and the US. It’s also the largest freshwater lake in the world.

Top image: an aerial view of the Caspian Sea. Credit: Alireza Akhlaghi/Getty Images