A pedestrian strolling along the banks of the Lez River in Montpellier might be fooled into thinking the water is peaceful. Ducks float calmly, and the surface appears still, but beneath lies a surprising and potentially disruptive presence: the African catfish. This large, invasive species has found its way into the river, likely after being released by private individuals who struggled with its impressive size and growth. The African catfish (Clarias gariepinus) can survive out of water thanks to a specialized organ that allows it to breathe air, a feature that makes it highly adaptable to various environments. The African catfish, also known as the large African catfish, belongs to the Clariidae family. It is identifiable by its four pairs of barbels around its head, a rounded snout, and a single dorsal fin that extends to the caudal fin, with a similarly long anal fin. While the average size is about 90 centimeters, some individuals have grown up to 1.70 meters long and weighed nearly 60 kilograms. This makes it unsuitable for home aquariums, even large ones, as it outgrows most setups quickly. Native to a wide range stretching from Guinea to the Cape Province in South Africa, passing through several Middle Eastern countries, the African catfish was introduced to Europe for aquaculture. Its rapid growth, ability to thrive on inexpensive agricultural by-products, and tolerance for oxygen-poor environments made it an attractive candidate for farming. However, this same resilience has led to its spread beyond its natural range. Many private owners, who initially purchased young fish without considering their eventual size, ended up releasing them into local waterways when they became too large to manage. This is likely how the species found its way into the Lez, where it has established itself in the urban river that flows through Montpellier. The African catfish is not only large and resilient but also an opportunistic, nocturnal predator that hunts mainly at dusk. It has a varied diet that includes insects, plankton, invertebrates, smaller fish, and even the young of birds or decaying flesh. This adaptability and lack of natural predators in Europe make it a formidable competitor for native species in the Lez. Its ability to survive in poor water conditions and its voracious appetite have led to ecological concerns in several countries where it has been introduced. The presence of this species in the Lez highlights how a single act—releasing a pet—can lead to significant ecological disruption. Efforts to monitor and manage such invasive species continue, but once established, complete eradication is often difficult to achieve.