Lake Sfânta Ana is the only crater lake in Romania, located in the volcanic crater of Ciomatu Mare volcano in the Eastern Carpathians near Tușnad, Harghita County. Palynology studies date the formation of the lake between 9,800-8,800 years ago as a peat bog and shallow lake. The oval-shaped lake has an area of 220,000 square meters and reaches a maximum depth of 6.4 meters, with sediment thickness of about 4 meters. Fed solely by precipitation, the lake water has a very low mineral content, almost as pure as distilled water. In winter, the lake is covered by up to 1 meter of ice.

1. Mocanu Andrei-Alexandru, MIEADR, Group 8115
University of Agronomic Sciences and Veterinary Medicine of
Bucharest 2018
Lake Sfânta Ana (Romanian pronunciation: [ˈsfɨnta ˈana]; Hungarian: Szent
Anna-tó, meaning "Saint Anne Lake" in both languages) is the only crater
lake in Romania] located in the volcanic crater of the volcano
named Ciomatu Mare of the Eastern Carpathians, near Tușnad in the Natural
Reserve of Mohoș, Harghita County, Romania.
Palynology studies concluded that the history of Lake Saint Anne began
about 9,800-8,800 years ago, at the stage of peat bog and shallow lake.
It has an oval form and an area of 220,000 m².
According to measurements made in 2005, the maximum depth of the lake is
6.4 m and the sediment thickness is about 4 m. The lake is supplied
exclusively from precipitation, therefore the degree of mineralization of the
water is very low. The water purity approaches of that of distilled water,
with only 0.0029 ml mineral
In winter, the lake is covered with a layer of ice of up to 1 m. The lake is part
of the Mohos Nature Reserve.
Acknowlegments:
Coordinating Teacher
Mihai Daniel Frumușelu
References:
https://en.wikipedia
.org/wiki/Lake_Sf%
C3%A2nta_Ana