The Sea of Marmara, also known as the Marmara Sea, is an inland sea located entirely within the borders of Turkey. It connects the Black Sea to the Aegean Sea via the Bosphorus and Dardanelles straits, separating the country’s European and Asian sides. The Sea of Marmara is a small sea with an area of 11,350 km2, and dimensions of 280 km × 80 km. Its greatest depth is 1,370 m.
The surface salinity of the Marmara averages about 22 parts per thousand, which is slightly more than that of the Black Sea, but only about two-thirds of that of most oceans. The water is much more saline at the bottom of the sea, averaging a salinity of around 38 parts per thousand, similar to that of the Mediterranean Sea. This high-density saline water does not migrate to the surface as is also the case with the Black Sea, Water from the Susurluk, Biga (Granicus), and Gönen Rivers also reduces the salinity of the sea, though with less effect than on the Black Sea. With little land in Thrace draining southward, almost all of these rivers flow from Anatolia.
The sea’s south coast is heavily indented and includes the Gulf of İzmit, the Gulf of Gemlik, the Gulf of Bandırma, and the Gulf of Erdek.
In Greek mythology, a storm on the Propontis brought the Argonauts back to an island they had left, precipitating a battle in which either Jason or Heracles killed King Cyzicus, who mistook them for his Pelasgian enemies.
According to Wikipedia