Puentes Viejas Reservoir, Reservoir in the Sierra Norte, Community of Madrid, Spain

Puentes Viejas Reservoir is a water reservoir in the northern part of the Community of Madrid, set among the hills of the Sierra Norte. It is fed by the Lozoya River and surrounded by wooded slopes that reach down to the water's edge.

The reservoir was planned from 1907, when Canal de Isabel II director Ramón de Aguinaga calculated a need for 30 hm³ more storage; the project was drafted in 1910. Work began in 1914 on a 44-metre dam, raised from 1932 to its final height in 1935. Construction stopped during the Civil War, when the water was kept high for tactical military reasons despite restrictions on Madrid's supply, and the surface spillway closures were only fitted in the early 1960s.

The name of the reservoir refers to old bridges that once crossed the valley and now lie beneath the water. Along the shores, small villages remain where the rural life of the Sierra Norte is still part of everyday reality.

The trails around the reservoir vary in difficulty, so it is worth checking the route before setting out. Comfortable shoes and enough water are a good idea, especially in summer when the heat can build up quickly.

When the water level drops significantly, the foundations of old bridges and structures that were flooded when the reservoir was built emerge from the surface. This is a direct reminder that an entire valley was submerged beneath the water.