The Yesa reservoir, in the municipality of Yesa, is fed by the river Aragon and the river Esca. Opened in 1960, it is 10 kilometres long by 1-2.5 kilometres wide and has capacity for 470 km3 of water.
Although there are no signposted hiking trails, it is a great place for walks along the shore and surrounding areas, keeping the reservoir as a point of reference. If you have time, you can encircle it on the northern side as far as its tail, under the formidable limestone outcrop of the Sierra de Leire
; and if you go further into the green undergrowth, on peaceful days you can hear blackbirds and robins singing or the elusive sounds of mountain cats, hares, foxes, dormice, weasels and genets.
The dam, further upriver close to the town of Yesa, is 400 metres long and 75 metres high.
In Yesa you can visit the remains of the Roncaleses bridge
over the river Aragon, which was built at the end of the 11th century. Seventy metres long by two and a half wide, it still has three of its five original Roman arches. Its name stems from the belief that there was a decisive battle here against Arab troops at the beginning of the Reconquest, in which the inhabitants of the Roncal valley took part. The battle is reflected in the valley's coat of arms.
Near the reservoir you can visit Sangüesa
, a monumental city crossed by the Pilgrim's Way to Santiago, or the Castle of Javier
where the patron saint of Navarre, St Francis Xavier, was born. If you like the idea of listening to Gregorian chant in a medieval building perched at the top of a mountain, make sure you visit the Monastery of Leire
. From there you will also get a magnificent view of the Yesa reservoir.