From: http://www.pbase.com/lambsfeathers/t_central1994
This waterhole in the Ormiston Gorge is separated from any other water except in
floods which occur only every few years. Then it becomes part of the Finke River,
and the fish - and there are lots of them - meet up with their distant cousins.

But see what happens when it dries up: http://pbase.com/image/64196598 et seq.