48.8% of the reservoirs in the Basque Country are filled, almost 6 points less than usual in August

The reservoirs of the Basque Country are in a delicate situation. The filling levels of the main torrents are lower than those of a year ago and are well below the historical average of the last two decades; the drop in rainfall and high temperatures have affected the water reserves of the territory this summer.

The highest level of water harvestinginthe last two years was reached in May 2025, reaching 94%, 10 points higher than normal (in the last 20 years this level has only been exceeded on 11 June 2013); a year later, on 19 May 2026, the reserves were 90.8% , also above average.

This year, 25 August 2026 , the global hydraulic reserve in the Basque Country has 626 cubic hectometers (hm³), according to data from the Ministry for the Ecological Transition and the Demographic Challenge. This means that our reservoirs have 48.4% of their capacity capacity covered; iaz, at the same time, the level was 719 hmm (55.6%).

The reservoirs of the Southern Basque Country, according to the bulletin of the Ministry, are divided into three watersheds: those of the interior of the Basque Country, those of the eastern Cantabrian (including Ordunte, Burgos) and those of the Ebro basin (including Cantabria, Castilla y León, La Rioja, Castilla-La Mancha, Aragón and Catalonia).

High pressure in the Ebro basin

The largest contribution and volume of thesystem is in the reservoirs of Esa ko (most of Zaragoza) and Itoiz, both in Navarre, which currently have 157 and 183 hm³ respectively, with a significant decrease from last year's data.

It also stands out for its capacity, Ullibarri-Gamboa in Álava, which according to the latest data is now 102 hm³ (a year ago it was 108 hmm), Urrunagain Álava (48 hmm now 52 hmm a year ago) and Allotzin Navarre (40 hmm; last year 49 hmm).

At present, Navarre has the most critical situationin our territory, with 42.9% of the filling of its reservoirs. The situation of its two giants determines the balance: 35.1% of the ESA and 43.9% of Itoitz, which was 56.3% a year ago.

The Basque Autonomous Community, for its part, has a calmer level, 69.4%, but 5.5 points less than at the end of August last year.

Irabia, the only exception that has improved figures

At present, most reservoirs are below the percentages of a year ago, with the only positive exception of the entire network being the small Irabia reservoir in Navarre, which currently retains 7 hm³, whichis half its capacity, since it has two cubic hectometers more than at the same time last year, that is, it has earned more than 14 points (35.7%).

On the other hand, smaller reservoirs such as Albina, Nagore, Urdalur and Endara have the same records, while the rest of the infrastructure continues to decline.

Highs in spring, lows in autumn

The seasons significantly mark the performance of the Basque basins, so thatthe reserve usually peaks between May and June, on a year-on-year basis: in the last 20 years the historical average is 83.2% in May, due to the melting of the ice and heavy spring rainfall, followed by the collapse from October to November and the beginning ofa significant decline, with an average reserve in October of 42.3%.

Despite annual oscillations, the historical series highlights the alternation of hard dry periods with rapid restoration phases, notably the minimum of November 1, 2011, when reserves fell to 30.3% . Then the system went through two other notable dry periods between 2016 and 2017 (lows close to 31.3% at the end of 2016 and annual averages close to 57%) and in the 2022-2023 cycle, the average annual reserve was 59.8%, almost seven points below the overall average of the last 20 years (66.4%).

Despite the episodes of water stress, the Basque reservoir network has shown great recovery capacity in the wet years, such as the rapid recovery of 2013-2014, with an annual average of 76.5% after touching the historic compliance ceiling on 11 June 2013 (reserves reached 95.4%) and 2025, when the reservoirs exceeded 94% on 20 May.