Mr Strel's swim also covers parts of the Danube that were affected by a major pollution spill last winter.

BBC: Minister takes the Danube plunge

Strel, the Slovenian who has also swum the Yangtze, Mississippi and Danube, says the Nile is on his to-do list.

BBC: What adventures are actually left?

Strel plans to swim across the Grand Canyon , along 1, 000 miles of the freezing Mackenzie River in Canada, and the length of the 2, 000-mile Volga .

BBC: What adventures are actually left?

Mr Strel, who is campaigning for the World Wide Fund for Nature, began his swim in Germany in June and hopes to reach Sulina on the shores of the Black Sea.

BBC: Minister takes the Danube plunge