A Hull man hoping to become the first person to complete an unbroken walk around the world is planning a 186-mile (300km) swim across the Caspian Sea, according to BBC.
Karl Bushby set off in 1998 and is more than two-thirds into his 36,000-mile (58,000km) adventure.
However, he said tensions between the West and Russia and Iran have meant the only option open to him if he wants to continue is to swim from Kazakhstan to Azerbaijan.
The ex-paratrooper said: "This is the best route, because it's the only viable route. Failure here would be crippling."
Under the rules he set himself before beginning his adventure, which he has called the Goliath Expedition, Mr Bushby must not use any form of transport.
According to his research, no-one has ever swam across the Caspian Sea - the biggest enclosed, inland body of water in the world.
He said he intends to set off on the swim in mid August.
Backed up by a support boat, he will be joined in the water by two members of Azerbaijan's national swimming team.
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