It does not exceed three centimeters in length and seems harmless, but it is one of the hundred most harmful invasive species on the planet. It is the zebra mussel, which arrived in Catalonia 25 years ago and is fully established in the Catalan Ebro basin – in the Riba-roja and Flix reservoirs up to the river's headwaters – and in the Llobregat basin, in the La Baells reservoir. Experts admit that eradicating it from these colonized areas is now impossible, which is why they focus on preventing it from spreading to other basins, a growing risk due to its high colonization capacity. "A point is reached where we can only aim for containment," warns Joan Pino, director of the Centre for Ecological Research and Forestry Applications (CREAF), who explains that one of the main negative impacts of this species is that it clogs the pipes of water systems in river systems. In fact, this week Aitona was left for 24 hours without a supply of drinking water due to this invasive species, which had collapsed the water treatment plant.