What disinformation narratives have gone viral: that the “destruction of reservoirs and dams in recent years” is responsible for the the DANA (the Spanish acronym for high-altitude isolated depression, a weather phenomenon that recently caused serious flooding in Valencia and other eastern regions of Spain) and that, if they were still standing, the consequences would not be as severe.
The reality: neither reservoirs nor large dams have been destroyed in the Júcar river basin, the area most affected by the floods and which includes the province of Valencia. The weirs demolished in the Júcar Hydrographic Demarcation were removed between 2006 and 2021 (the latest year available in data from the Ministry for the Ecological Transition and Demographic Challenge), under governments of various political affiliations (Aznar, Zapatero, Rajoy, and Sánchez). In the province of Valencia, the only barriers demolished were taken down between 2006 and 2017, before Pedro Sánchez’s first government (2018).
What can be explained: it is not possible to verify what would have happened if the hypothetical world imagined by these narratives existed. However, we can explain that weirs and small dams, not reservoirs or large dams, have been demolished, and they are removed for flood safety, legal obligations, and ecosystem restoration. Not removing obsolete or poorly maintained weirs poses a greater flood risk because it raises water levels in uncontrolled areas and can create blockages, according to two experts.
What infrastructures have been removed in the area affected by the DANA phenomenon in Valencia and why we know they are not large dams or reservoirs
Some messages from this narrative claim that "dams and reservoirs" are being destroyed. They also suggest that this is being done at the request of the European Union. This is false.
What has been destroyed, at least since the year 2000, are small river barriers: structures that interrupt the flow of rivers and are mostly weirs and small dams only a few meters high that have become obsolete or are no longer in use. These structures do not retain water like a reservoir does; instead, they were used to raise the water level and divert the flow to other places, for example, to facilitate the irrigation of nearby plots. In this article by Maldita.es, we explain the infrastructures demolished in the province of Valencia to debunk the claim that "four reservoirs have been demolished."
The Ministry for the Ecological Transition and Demographic Challenge (MITECO) publishes the number of infrastructures removed by hydrographic demarcation and year. In the case of the Júcar River Basin, the most affected by these floods and where the province of Valencia is located, 28 infrastructures have been demolished since the year 2000. On MITECO's geoportal, it is possible to see each of these infrastructures along with the date of demolition, the use of the structure, and its height; in some cases, observations are provided on who funded the demolition or the reason for it. None of these infrastructures were dams or reservoirs.
The tallest infrastructure among those demolished is the El Retorno weir, measuring 7.35 meters, a considerable height but still less than the dams of the smallest reservoirs in the Júcar: El Regajo (6 hm³, with a 28-meter dam) and Algar (6 hm³, with a 49-meter dam).
Additionally, there are six demolished structures that are referred to as "dam of": Albaladejito, La Hoz, Las Hoyas, Las Pericas, Los Garridos, and Narboneta. None of these structures were reservoir dams, as can be seen on both MITECO's geoportal and Google Maps images (with links to where each structure was located).
Furthermore, in Maldita.es, we explain the infrastructures specifically demolished in the province of Valencia to refute claims that “four reservoirs have been demolished.”
Who is responsible for removing these barriers: neither President Sánchez nor the European Union, but the river basin organizations
Some content places the blame on the Sánchez government or the European Union for the demolition of these weirs or small dams. Firstly, the demolition of these barriers is a decision made by the river basin organizations, the institutions that manage water use within river basins (areas through which a main river and its tributaries flow).
Regarding the content that points out that Sánchez’s Government has destroyed dams and that is why there are more deaths due to the floods in Valencia, no dam, reservoir or weir has been demolished between 2018 and 2024 in the area affected. In addition, neither reservoirs nor large dams have been destroyed in the entire Júcar Hydrographic Demarcation.
Some of these institutions are dependent on a regional government (if the basin is located within a single autonomous community) or on hydrographic confederations (if the basin spans multiple communities, such as the Júcar basin).
Most of these demolitions are decided by each river basin organization, as explained to Maldita.es by the Cantabrian Hydrographic Confederation, although in some cases, the decision may come from the Directorate General for Water, an agency within MITECO.
Additionally, these demolitions have been carried out throughout Spain since at least the year 2000 (under the Aznar government, PP). In the Júcar basin, these demolitions have been taking place from 2006 to 2021, under central governments of different political affiliations (Zapatero, Rajoy, and Sánchez). Specifically, in the case of the infrastructures demolished in the province of Valencia, they occurred between 2006 and 2017, before the arrival of the Sánchez government.
Why disused weirs and small dams are removed: safety, legal obligation, and ecological restoration
One reason these barriers are removed is precisely to prevent risks during heavy rainfall. Keeping small, disused structures or those in poor condition can increase the risk of flooding because they raise the water level in uncontrolled areas and can cause a river to overflow, explained Arturo Elósegi, a professor of River Ecology at the University of the Basque Country, in El Confidencial. Removing these river barriers “does not worsen flooding; rather, it reduces it, as it prevents blockages that could force water out of its channel,” Elósegi detailed in EFE Verifica.
The 2023 report by the organization Dam Removal Europe explained that these river barriers can create strong underground currents in their vicinity, and there have been over a thousand documented drownings in the United States over the past 20 years as a consequence of these infrastructures.
Another reason for removing barriers is due to legal obligation. The Hydraulic Public Domain Regulations establish that river basin organizations must remove infrastructures that are "abandoned, not serving any function related to the use of water." Barriers may also be removed if they were installed without the proper permits, as has happened in some cases in the Júcar basin, where weirs had to be removed due to administrative sanctions.
A third reason is that removing these obstacles promotes the continuity of rivers and allows water, sediments, fish, and other species to move freely through the basins, as explained by the European Environment Agency. This has a positive impact on water quality. These measures also help maintain river ecosystems in good condition and protect biodiversity, as noted by MITECO. This benefits, for instance, fish populations, providing both ecological and economic advantages (fishing).
We have also asked several experts to explain whether, in any case, river weirs could help reduce flooding, and we will update once responses are available.
