Iceland: Swimming in the 'world's clearest waters' - BBC Travel Show

Cat Moh goes for a dip in the icy waters of Silfra - the only place in the world where you can dive or snorkel in a crack between two tectonic plates.

The earthquakes of 1789 opened up several fissures in the Thingvellir area, but this one cut into the underground spring filled with glacial meltwater from the nearby Langjökull glacier.