We were floating right above Cousteau’s barrier in the middle of Kozjak Lake. We dived to its edge, from where like the wall of a twenty-storey building it fell away into the darkness below. For a while I floated weightless parallel to the deepest side of the barrier, which looked like a kind of underwater Taj Mahal, whose builders this time, instead of human hands, were travertine moss and blue green algae.
Chub and pearl roach, species of carp that amongst other things eat the spawn of other fish, have forced out the trout from most habitats in the Plitvice Lakes National Park. But scientists have not yet found an answer to the question whether any species of fish is actually native to the lakes, or were they were all introduced by human hand during the 20th century. Research into their genetic origins may resolve this puzzle.