Reservoir that stores and channels water from the Ter River and is located within the Guilleries-Savassona Natural Area. It is an excellent place for hiking, observing flora and fauna and practicing water sports. Although the original project to build the reservoir dates back to 1931, works on the Sau marsh did not begin until 1942. They were finished in 1966 and caused a major alteration to the landscape. One of the best-known prints in the marsh occurs when the water level drops and the bell tower of Sant Romà de Sau appears. Over time it has been seen that, in addition to producing electricity, storing and channeling the water of the Ter River, the swamp is a first-class tourist resource, since every year it receives thousands of visitors who come to enjoy the Les Guilleries-Savassona Natural Area for swimming or practicing water sports such as rowing, sailing or water skiing.