The salinity of the sea averages about 22 parts per thousand. This is slightly greater than that of the Black Sea but only about two-thirds that of most oceans. The water is much more saline at the sea-bottom, averaging salinities of around 38 parts per thousand — similar to that of the Mediterranean Sea. Water from the Susurluk, Biga (Granicus) and Gonen Rivers reduces the salinity of the sea.