Lac Hertel lies at the heart of the mountain. It has an area of 0.3 km2 and a maximum depth of 9 metres (about 30 feet). The lake was formed by the glaciers that covered the mountain about 10,000 years ago. Lac Hertel is fed by three year-round streams and drained in the south by a fourth. Every spring and fall, hundreds of Canada geese take off from the waters of Lac Hertel. The lake is also populated by about ten species of fish, including pike, rock bass and yellow perch.