Lake Hévíz is the largest thermal lake on Earth that you can swim in, and it replaces itself every three and a half days. The spring that does it opens in a cave thirty-eight metres down, in western Hungary, and it pushes water up fast enough that nothing in the basin ever gets cold. The lake has no winter. When the air outside drops below zero the surface throws off dense steam and you swim inside a white fog, with the far bank and the turret of the old bath house appearing and vanishing in it. You are warm to the shoulders and cold on the scalp. Almost nobody here swims lengths. You take a rubber ring, work out over water far too deep to stand in, and hang there drifting with everybody else, an hour at a time.
Everything living in it runs on the same broken clock. The water lilies were an experiment. A professor from the academy at nearby Keszthely put tropical species in during 1898, to see whether the warm water would carry them through a Hungarian winter. The Indian lily took and is still here; the Egyptian lotus and the blue varieties died out. The rafts do not stay put — a stand drifts off and re-establishes itself somewhere else every few years. They cover much of the open surface from summer into late autumn, and the flowers open in the morning and shut as the day warms. Nothing could be built on the shore, which was quaking bog and reed, so the baths were carried out over the water on larch piles driven into the bed, the way Venice stands on its own. Gas rising with the thermal water has been eating the tops of those piles, and the old bath house has been shut since 2025. Below it the lake's dwarf carp reach breeding age in about a year, where Hungarian carp need four or five. They spawn in February, while the rest of the country is frozen, and they lay their eggs on the undersides of the lily leaves.