Fish fauna confirms the recovery of river connectivity in Artikutza after the dam was emptied
11/11/2025
Monitoring carried out by Donostia/San Sebastian City Council has revealed that the restoration of the reservoir has re-established the natural connection between brown trout populations and other native species.
The ecological restoration work carried out in the area around the Enobieta reservoir in Artikutza continues to produce positive results. Donostia/San Sebastian City Council carried out four campaigns between 2017 and 2025 to monitor the fish community in the Artikutza and Enobieta watercourses, with the aim of analysing the effects of emptying the dam and assessing the evolution of the river ecosystem.
Sampling was carried out using electrofishing, following the methodology used by the Provincial Council of Gipuzkoa and the Government of Navarre, and identified a significant improvement in the connectivity of the river system. The samples were taken at four stations located both upstream and downstream of the main dam, including a station next to a small dam that appeared after the dam was emptied and was subsequently removed. Populations of minnow (Phoxinus bigerri), brown trout (Salmo trutta) and a few specimens of European river crayfish (Austropotamobius pallipes) are showing remarkable recovery and expanding.
The results show clear changes in the distribution of species. The minnow (Phoxinus bigerri) and the European river crayfish (Austropotamobius pallipes), were only found upstream of the dam when the studies started, but now also occupy the downstream areas. The brown trout (Salmo trutta) has managed to colonise all of the sampling stations and was found in high densities.
This means that the two previously isolated trout populations, one upstream and one downstream of the old reservoir, are now connected. Fry produced in the upper section of the forest are now able to disperse throughout the river system, and adults, which were previously unable to swim upstream to this section, can now travel upstream and breed there. Overall, this union of nuclei represents a significant change in trout population dynamics, restoring the Artikutza-Enobieta system to a more natural state.
The naturalisation of the environment is progressing steadily: the Enobieta stream continues to recover its original course and structure, and vegetation is steadily increasing.
These actions are part of the actions promoted as part of the LIFE IP Urban Klima 2050 project, which promotes nature-based solutions in river basins to adapt the Basque territory to climate change and improve the resilience of its ecosystems.
