The Sau reservoir is a Spanish hydraulic infrastructure built on the Ter river, located in the municipality of Vilanova de Sau, at the foot of the Guilleries massif, in the Osona region, province of Barcelona, Catalonia.
It is part of a system of three reservoirs, together with those of Susqueda and Pasteral, which joins the counties of Osona and La Selva. The reservoir, inaugurated in 1962, covered the town of San Román de Sau, the remains of which, especially the bell tower of the temple, are visible when the water level is low and, even in times of prolonged drought, the town is left to the discovered and it is possible to visit it.
The church of the Sau swamp is registered as the oldest in the world that is preserved standing in the water. [2] This is confirmed by a study promoted by the international entity of world record records Official World Record with the collaboration of a research group from the University of Barcelona in the year 2021.