Xerta weir on the River Ebro, Spain, July 2024. This is the first major barrier for upstream migrating fish on this river, and it is located approximately 56 km from the sea. Construction of a new fish pass was underway at the time of my visit, with the ongoing works apparent in the video. The fish pass will be a rock ramp-type channel leading from the tailrace to above the weir. While it won’t solve all the fish passage problems at this site, it will be a significant improvement over the previous situation. Other measures being implemented at this site include fish-friendly management of the ship lock and the installation of a dedicated fish lock.

There has been a weir at this site since the 12th century. However, it was not finished until the early 15th century. The irrigation canal and boat lock were added in the 1850s, with an additional canal on the left bank constructed in the early 1900s. The 18 MW hydroelectric scheme was completed in 2002. A pool pass was installed in 2008, but it never worked effectively. This was due to the entrance being on a different channel away from the main flow in the tailrace, along with the high turbulence and flows in the pass itself.

The irrigation canals supply a vast agricultural area, including the rice paddy fields of the Ebro delta. Downstream migrating fish can still enter both the turbines and irrigation canals. However, there are plans to also address this problem in the future. It is hoped that the new fish pass will facilitate the upstream migration of #eels, shad, and lampreys. Efforts are also underway to restore European sturgeon to the river.

The next weir upstream from here is Ascó weir, and a new rock ramp fishway has also recently been installed at this site. Further upstream, there are three major hydroelectric dams (Flix, Riba-roja, and Mequinenza). Fish passage improvements at these dams are also planned, and fish-friendly improved management of the ship lock at Flix Dam has already been implemented. However, restoring fish passage at these dams will be far more challenging.

The upper Mequinenza dam lies approximately 160 km from the sea, and historically sturgeon accessed the Ebro as far upstream as Tudela, located over 490 km from the sea. In December 2023, juvenile sturgeon were restocked into the River Ebro downstream of Xerta weir as part of the restoration project. It is hoped that the fish passage improvement works currently underway will have been successfully implemented before these fish (hopefully) return.

Restoring rivers is not easy, and there are an estimated 190 significant fish migration barriers in the River Ebro catchment, indicating the scale of the problem. The restoration efforts here are set against the background of water quality decline, over-abstraction of water, climate change, and invasive species, to name a few other pressures. But to hold on to what we still have, we have to try for the impossible.

Conditions are unlikely to ever be suitable again for sturgeon to reach Tudela, but having a small, self-sustaining population in the lower River Ebro would be a major success story. Furthermore, the fish passage improvements will greatly benefit eels, sea lampreys, and shad. These species are likely to be regularly seen upstream as far as the Flix Dam, and potentially even further into this major European catchment in the near future.

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