Zebra mussels threaten Spain's water infrastructure with massive pipe blockages

In northeastern Spain, invasive zebra mussels are clogging irrigation canals and water pipes, with densities up to 40,000 per square meter, prompting experts to call for long-term mitigation measures.

Zebra mussels, a freshwater bivalve native to the Ponto-Caspian region, were first detected in Spain's Ribarroja Reservoir in 2001 and have since proliferated throughout the Ebro River basin, reaching reservoirs such as Santa Anna, Canelles, Escales, Oliana and Terradets. Their extraordinary reproductive output allows colonies of 10,000 to 40,000 individuals per square meter to develop, causing total blockages in pipes under half a meter and reducing flow in larger conduits by 60-70 percent.

Experts note that dead shells cling to pipe interiors, so simply eradicating live mussels does not restore functionality. Biologist Antoni Palau suggests adapting infrastructure by building redundant lines and scheduling annual drying of water bodies to hinder colonisation. A 2026 study in the Journal of Hydraulic Research modeled shell transport to help design traps and flushing regimes. Authorities estimate the invasion could cost tens of millions of euros over the coming decades, with no definitive solution yet available.