Lake Saint Anne is the only volcanic lake in the whole territory of Romania. It is located in county Harghita, in the crater formed at the summit of Mount Ciomatu, on the left side of the valley of the river Olt, near Tușnad. The lake is situated in the crater of the dead volcano, namely Ciomatu (or, according to other sources, Ciomadu), from the volcanic Mountain Pucioșu, the place of the most recent volcanic activities in the Carpathians and in Eastern Europe, which had taken place more than ten thousand years ago (probably 42.0000 years ago). The surface of Lake Saint Anne is about 946 m above sea level. The shape of the lake resembles a palette, having an almost circular form, the shore of the lake is 620 m long, 460 m wide and 7 m depth. Its surface measures 19,50 ha. The lake does not have other sources of inflow than precipitation. The water of the lake was claimed to have a mineral content similar to that of distilled water, with only 0,0029 ml mineral content. The reduced trophic capacity of the lake’s water is due to the gas emissions from the bottom of the lake and through the crater’s rim. The visitors of the Lake Saint Anne do not need any weather forecast of the meteorologists, in order to find out the weather. They had at disposal an empirical, but at the same time an exact method, offered by the volcanic mountain: the two fissures formed in the mountains, which are forecasting the weather. The local inhabitants know “If the emissions from the fissure sting the nose, that means it will be stormy, but if not, it will be a fine sunny day, suitable for mountain hiking”. This phenomenon has a scientific explanation. The mountain still has a post-volcanic activity, which is sensible to any change of the atmospheric pressure. When the atmospheric pressure is law, the gases, like carbon dioxide and sulfur rise to the surface and inundate the fissures with a sharp smell, which is a sign for rainy weather.