The presence of shells of the Atlantic rangia, Rangia cuneata, a brackish-water species native from the Gulf of Mexico also known as gulf wedge clam, was reported in 2017 on the French coasts of the English Channel, in the waterway that connects Caen to the sea. However, no information was available on whether a population of this alien species had successfully established in the region. Here, only empty shells—except for one live individual—were sampled in that waterway, and the sampling was shifted to the nearby marina of Ouistreham, where water is mesohaline (6.89 ± SD 0.06 PSU). In spring 2017, the mean density in the marina reached 110.45 ± 86.08 ind m-2, largely dominating the benthos community. The population was mostly composed of fairly large individuals, with no young-of-the-year found inside the marina. The modal values of the size frequency distribution ranged between 35 and 40 mm shell length. The growth patterns determined from the annual rings suggest a maximum lifespan of eight completed years. Following the assumption that colonization occurred at the larval stage, as in other European countries, this population may have established in 2009, i.e. only four years after its first detection in Europe, in the Antwerp harbour. The specimens collected are the largest recorded in European waters, suggesting a highly suitable environment for the species in the region. Given the invasive potential of Atlantic rangia within the last decade, a close monitoring of this population and of the spread of the species in French and European waters appears necessary to determine its impacts on these ecosystems.