The sea lamprey (Petromyzon marinus Linnaeus, 1758) has a vast distribution area, including both shores of the Northern Atlantic and the Mediterranean Sea. It is commonly assumed to be present in Morocco, but the only specific records of the sea lamprey in the country come from the first half of the 20th and are exclusive to the Atlantic coast. Here we report the presence of adult sea lampreys in Oued Moulouya, the largest of the Moroccan rivers flowing to the Mediterranean Sea. We stress the need to develop studies on the ecology of this river, which could be important for the sea lamprey and other diadromous fish, such as the poorly known shad Alosa algeriensis Regan, 1916.