Spain’s zebra mussels reach 40,000 per sq metre, damaging pipes and structures

In northeastern Spain, the spread of zebra mussels continues to baffle water management experts, keeping them on alert over the damage to water infrastructure caused by these invasive species. Their presence in reservoirs, irrigation canals and water distribution networks has begun to disrupt water supplies, especially in Catalonia's Lleida province, as per a report by Diario AS. According to specialists who have been tracking the spread of the species for more than two decades, long-term structural measures need to be deployed in order to curb their advance further.An unchecked expansionZebra mussels (Dreissena polymorpha) are a freshwater bivalve native to the Ponto-Caspian region that has spread across much of Europe and North America. It first arrived in Spain in 2001 when they were discovered in the Ribarroja Reservoir along the Ebro River. Genetic studies indicate they originated from France, crossing the Pyrenees barrier via recreational boat hulls or live fish transport.It is their extraordinary reproductive capacity that allows them to colonise aquatic systems at remarkable speed. A single adult can produce between 400,000 and one million gametes during the spring and fall breeding seasons, when water temperatures range between 55 and 60 degrees Fahrenheit. Its larvae, measuring just 200 microns, are carried by water through rivers, reservoirs, canals, and pipelines, where they mature to roughly 1.5 inches in about a year.The Ebro River Basin Authority recently confirmed the presence of adult zebra mussels in the Santa Anna Reservoir, while repeated detections of larvae have been recorded in Canelles, along with signs of the species in the Escales, Oliana, and Terradets reservoirs. Specialists, moreover, believe the invasion has already spread across significant portions of irrigation systems not only in Catalonia, but also in the Spanish region of Aragón, and has also reached drinking water distribution networks.The impact on infrastructure has been particularly severe. In some irrigation ponds, densities of between 10,000 and 40,000 mussels per square meter have been recorded. In pipelines with diameters smaller than half a meter, blockages are often total. Even in larger conduits, hydraulic capacity losses can reach 60% to 70%, significantly undermining the efficiency and performance of water delivery systems.Coexist with the enemyAntoni Palau, a biologist and professor at the University of Lleida, believes that living alongside the species is now “inevitable” and argues that the only viable solution is to adapt infrastructure to this new reality. Among the key measures he proposes are duplicating certain facilities so pipelines and conduits can be cleaned and repaired without interrupting water service, as well as establishing annual draining and drying periods for reservoirs, tanks, and canal systems to help slow the mollusc’s spread.Palau notes that removing adult specimens does not solve the problem, because blockages continue to occur as a result of the shells attached to the walls of pipes and conduits. These remain firmly fixed in place even after the animal dies, reducing water flow and damaging the performance of valves, pipelines, and other components of hydraulic systems.A 2026 research paper published in the Journal of Hydraulic Research investigated the movement, velocity, and dispersion dynamics of detached zebra mussel shells in pressurised pipelines under varying flow conditions. This is because detached shells flowing through irrigation and water distribution networks cause operational issues such as pipe blockages, reduced flow efficiency, and filter clogging. The calibrated model parameters provided a framework for predicting shell transport and accumulation zones (such as dead zones) in pressurised irrigation networks, aiding in the design of shell traps and flushing protocols.In a 2011 study published in Science News, Project leader Professor Amparo Torreblanca of the Department of Functional Biology and Physical Anthropology recalled that invasion of this species since the eighties has cost the United States millions of dollars, while the Confederación Hidrográfica del Ebro predicted in 2005 that the zebra mussel expansion would cost about 40 million Euros over twenty years. This is because the mollusc "creates significant problems and economic costs due to its ability to block all types of infrastructure and water pipes," added the professor.Currently, there is no ideal solution to rectify this expansion and help recover the damaged infrastructure.