An aluminum processing plant, which is located at the Antikyra Bay, at the northern margin of Corinth Gulf, is producing a high radioactive contamination in the marine environment, due to the discharge of bauxitic red mud tailings. The levels and the distribution of 238U, 232Th, 226Ra, 40K and 137Cs in marine sediments of the area have been determined. The results indicate that the seafloor of Antikyra bay and the basin of Gulf of Corinth are highly contaminated with 238U, 232Th and 226Ra. On the contrary, the red mud tailings induce depletion to the 40K and 137Cs concentrations in the area.