A species of crab known as the Chinese mitten crab (Eriocheir sinensis) has been found in France since at least 1930, and it has since become well-established in major rivers such as the Seine, Loire, and Gironde. This crab is native to the rivers of China and is thought to have first arrived in Europe through ballast water — the water stored in the holds of cargo ships to stabilize them during travel. Scientists believe the crab reached European shores in Germany at the beginning of the 20th century and then spread across the continent through connected river systems. It was first recorded in France near Boulogne-sur-Mer in 1930 and has since become common in several major French rivers by the mid-20th century. The Chinese mitten crab is known for its unique behavior of digging extensive burrows into riverbanks, often reaching depths of up to 80 centimeters. This activity can weaken the soil, speed up erosion, and increase the risk of riverbank collapses and silt accumulation. Despite efforts to control its population through trapping and regulatory measures since the 1930s, the crab has remained a permanent part of the French river ecosystem. Its life cycle, known as catadromous, is similar to that of the eel — it spends most of its life in freshwater and then migrates to saltwater estuaries to reproduce. This pattern makes eradication difficult, as new generations of young crabs continuously move upstream from estuaries, re-establishing populations even after local control efforts. The presence of the Chinese mitten crab has raised environmental concerns, particularly regarding the stability of riverbanks and the possible weakening of levees and other structures. The crab is an omnivore, feeding on plants, small invertebrates, and fish eggs, which puts it in direct competition with native species like crayfish. Fishermen have also reported problems with the crab getting stuck in fishing nets, eating already caught fish, and clogging filtration systems in some industrial facilities. Despite these challenges, the Chinese mitten crab has experienced natural fluctuations in its population, which have prevented a dramatic surge in numbers. However, the long-term impact of its burrowing behavior on riverbank stability remains a concern, especially in the context of existing challenges related to flood management and changing water levels. The continued presence of the Chinese mitten crab in French rivers underscores the difficulty of controlling invasive species once they have become established in a new environment.