The Great Bitter Lake (Arabic: البحيرة المرة الكبرى; transliterated: al-Buhayrah al-Murra al-Kubra) is a salt water lake which is part of the Suez Canal. It is connected to the Small Bitter Lake (Arabic: البحيرة المرة الصغرى; transliterated: al-Buhayrah al-Murra as-Sughra), through which the canal also runs. Before the canal was built, their site was occupied by dry salt valleys. Together, the Bitter Lakes have a surface area of about 250 km². The canal also runs through Lake Manzala and Lake Timsah, north of the Bitter Lakes.
As the canal has no locks, sea water flows freely into the lake from the Mediterranean and the Red Sea. In general, north of the lakes the current reverses seasonally, being north-going in winter and south-going in summer. South of the lakes, the current is tidal, reversing with the tides in the Red Sea. Fish can migrate, generally in a northerly direction, through the canal and lakes in what is known as a Lessepsian migration. By this means some Red Sea species have come to colonize the eastern Mediterranean.
In the later part of World War II, the lake was used to intern Italian warships which had surrendered to the Allies, including the battleships Vittorio Veneto and Italia.
During the Six-Day War in 1967, the canal was closed, leaving 15 ships trapped in the lake until 1975. These ships became known as the "Yellow Fleet", because of the desert sands which soon covered their decks. A number of local postage stamps (or rather, decorative labels, since they had no postal validity) were created by the crews, which are sought after by collectors.