Located midway between Janzé and La Guerche de Bretagne, the lake at Marcillé Robert covers an area of 100 hectares. It is fed from south and west by two rivers, the Ardaine and Seiche, and was originally no more than a small reservoir hemmed in by a natural barrier of schist. To the west of the lake is a spur of rock created by Hercynian folding (which took place some 300,000,000 years ago) overlooking the entire valley.
