During the summer and autumn of 2018, ACCIONA-Energy carried out scheduled maintenance work on the Viana II (Viana, Navarre) hydroelectric power plant canal from the El Romeral waterway on the River Ebro.

The zone is at the upper limit of the distribution of the giant peral-mussel or margaritona (Margaritifera auricularia )The environmental administrations of Navarre and La Rioja authorized the extraction of the gravel that closed the passage of the water towards the canal, with the due measures of correction of the environmental impact and of vigilance in the work to avoid the death of some possible specimen located in that part of the riverbed of the Ebro.

In the weeks prior to the performance of the machines, a preventive exploration was carried out with professional divers in the deepest parts, and with routes on the wadeable shores to locate any sign of presence of the species, catalogued as “in critical danger of extinction” in Spain. During the presence of the vehicles in the riverbed and on the banks, new surveillance and possible rescue campaigns were carried out, as well as monitoring of the main water quality parameters that could be altered by these actions.

At the end of September the work was complete and the banks restored, but no evidence of the presence of giant pearl-mussel was found.o However, if very ancient remains of other naiads, of the species Potomida littoralis and Unio mancusbut no living specimen. The bed of the channel is environmentally highly transformed and invaded by other invasive exotic mollusks and crustaceans, such as the Asian clam –Corbicula fluminea– , el mejillón cebra –Dreissena polymorpha– y el cangrejo señal –Pacifastacus leniusculus-, entre otras.