Which sea is the saltiest, so salty that people float?

The Dead Sea runs to around 34 per cent dissolved salts, nearly ten times the ocean, which makes the water dense enough that a swimmer floats with very little effort. Almost nothing lives in it beyond some salt-tolerant microbes, which is where the name comes from.

It is that salty because it is a dead end. The Jordan flows in and nothing flows out; water leaves only by evaporating in the desert heat, and everything dissolved in it stays behind and concentrates. Its surface is also the lowest exposed land on Earth, some 430 metres below sea level.

It is disappearing. The Jordan's water is now largely taken for agriculture and drinking before it arrives, and the sea has dropped by more than thirty metres in fifty years, retreating so fast that the ground left behind collapses into thousands of sinkholes where buried salt layers dissolve. Beach hotels built at the waterline in the 1980s now stand well inland.