Lake Ohrid, on the border between North Macedonia and Albania, is one of the oldest lakes on Earth and clear enough that you can see twenty metres down. That clarity is borrowed from a mountain. Much of the water starts in Lake Prespa, 150 metres higher on the far side of Mount Galičica, which has no outlet and drains underground through cracked limestone instead. It takes months to work through the rock, and it arrives here cold and filtered. The lake has been filling this basin for more than a million years, long enough for over two hundred species to evolve in it and nowhere else, the Ohrid trout among them. Above the northern shore the town of Ohrid is stacked up the cliffs in white houses and red roofs.
A plank boardwalk pinned to the rock at the waterline runs from the old harbour round to Kaneo, the boards creaking underfoot while swimmers jump in off the rocks. At the end the thirteenth-century chapel of St John stands alone on a ledge above the water, and the terrace beside it looks out on the blue lake and the Albanian mountains beyond. You look over the rail and the bottom is still there under you. The narrow wooden boats leaving the harbour in the morning are working boats after that trout. It was fished so hard that catching it was banned for seven years. The catch now is counted rather than hauled. The stone lanes climb the other way to Samuel's Fortress, past a Hellenistic theatre the townspeople buried after the Romans used it for executions, and nobody found it again until the 1980s. The boats also run to the southern end, to the monastery of Saint Naum, where dozens of cold springs push up through the lakebed. On a calm day you can follow them down to the sand and watch them arrive, months after leaving the other lake.