To reach this resevoir, at the top of the Saas Valley, follow a small road from Saas Grund that offers beautiful views of the Saas-Fee glaciers. From the car park, allow 5min to reach the left end of the dam, which shows Stausee Mattmark Lake (1.76km²) surrounded by four glaciers (Hohlaub, Allalin, Schwarzberg and Seewjinen), from which many waterfalls descend. The lake has a capacity of 100 million m³ and a maximum depth of 117m. A path goes around it (2hr 30min).