Riaño Reservoir, Artificial reservoir in León Province, Spain

Riaño Reservoir is a man-made lake in León Province that stretches along the Esla River, surrounded by the Picos de Europa and forested slopes. The water reaches a maximum depth of roughly 100 meters (330 feet) and forms a long basin winding through narrow valleys, creating coves and rocky shoreline sections.

Construction began in 1965 and led to the relocation of nine villages, with residents moving to new settlements along the shore before the valley was flooded in 1987. The government planned the project for irrigation and power generation but faced resistance from local communities who left their homes.

The reservoir takes its name from Riaño, one of nine villages flooded when the gates closed on 31 December 1987. A new Riaño was built at Valcayo, above the water. In 2017 the MUSAC in León held an exhibition on the dam's impact on the region, and the documentary Mi Valle (2016) records memories of the valley.

A car is helpful for reaching different access points around the basin, though some shoreline sections can be reached on foot. Summer temperatures are mild, while in winter roads may occasionally close when snow blocks the higher passes.

When water levels drop, the foundations of some of the submerged villages emerge from the water, drawing photographers and history enthusiasts. The dam itself is roughly 337 meters (1105 feet) long and one of the largest concrete structures in this region of Spain.