The Tormes is a Spanish river, that starts in the Prado Tormejón, the Mountain range of Gredos, Navarredonda de Gredos, province of Ávila. It crosses the provinces of Avila and Salamanca, ending at the Duero river, the municipal term of Villarino of Airs (Salamanca), at the zone denominated locally as Ambasaguas, after 284 kilometres (176 mi) in length. Due to its characteristics this river does not provide the water supply to the population during summer and for this reason, at the end of 1960 the dam of Santa Teresa was constructed, with a capacity of 496 million cubic metres (402,000 acre·ft) that the water supply in summer assured and regulated as well as it laminated the great avenues at time of winter.