Every dam holding the sixteen Plitvice lakes apart is alive. They fall as a staircase through a wooded canyon in central Croatia. The barriers are travertine, and nothing laid them down but moss and algae, which pull lime out of the water until they harden into stone. They are still at it. The dams thicken by as much as a centimetre a year, and the oldest have been building for six or seven thousand years. Now and then one gives way and sends the water off on a new course, so no map of the lakes stays accurate for long. This is also why nobody swims here. The travertine is soft, and sunscreen and skin oils are enough to kill the organisms that make it, so the ban is exactly what keeps the water as clear as it is. Clear enough, where it pools above a dam, to count brown trout in the shallows and pick out tree trunks on the pale floor, sunk long ago and turned hard by the same lime.
The walk is laid on top of all this. Wooden boardwalks run a few inches above the surface, and in places the water slides under the planks before spilling over a travertine lip beside you. Cascades end up falling above and below you at once. The lower canyon ends at Veliki Slap, seventy-eight metres and the tallest waterfall in the country, with a platform at its foot where the fine spray settles on your face. Between the two halves of the staircase lies Kozjak, the largest lake, crossed by an electric ferry quiet enough to leave you the beech forest on the bank. Two months are worth choosing between. April carries more than three times the August flow and every barrier spills full; October turns the beech and hornbeam copper and doubles the colour in the still water below. Whichever you pick, nothing here is finished. The barrier you walk past will stand a centimetre higher next year, and sooner or later one of them will break and send the water somewhere else.