When the Aswan High Dam was built in the 1960s , this blocked the flow of freshwater from the Nile into the Mediterranean . The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of freshwater and nutrient-rich silt from the Nile into the eastern Mediterranean , making conditions in the eastern Mediterranean even more like the Red Sea , thus increasing the impact of the invasions and facilitating the occurrence of new ones .