Saint Guérin, patron saint of herds gave his name to the valley and the dam, which was built between 1957 and 1961. The dam contributes to feeding Lake Roselend through a connecting pipe between the reservoirs that operate in the manner of communicating vessels.
Its water surface is 50 hectares with a depth of 70m and a capacity of 13 million m3. Its arched-gravity structure measures 250m long. The reservoir receives each year the equivalent of twice its storage capacity.