Lake Hévíz is located in Hévíz, Hungary, near the western end of Lake Balaton, 8 kilometres (5 mi) from Keszhely.
It is the largest swimmable thermal lake in the world (47,500 square meters (511,286 sq ft) in area), second only the Frying Pan Lake in New Zealand, which is too hot for swimming. The flow of water is very strong and the water in the lake is completely replenished every 72 hours. Its minimum depth is 2 meters, reaching a maximum depth of 38 meters, exactly at the point where the hot thermal water comes out towards the surface.
In winter, the condensed steam forms a cap over the lake surface, creating a natural inhalatorium. This ‘cap’ prevents water from cooling down, rejuvenating exhausted vocal cords when inhaled. The lake developed in the same period as Lake Balaton, with its current source welling up 20-22,000 years ago. (In the geological past, Ancient Hévíz welled higher than its current location.) The lake was already used by the Ancient Romans. Several water-lily types inhabit the lake: the European white water lily is indigenous to the area, while the purple lily was brought from India 100 years ago. Thanks to an abundant water supply, the water of the 4.4 ha lake – with a depth of 38 m – is fully replaced every three days. Water quality is continuously controlled through measurements and specially trained divers.
