Swirls of color ranging from deep olive green to bright turquoise were created by a massive phytoplankton bloom that covered the entire surface of the Black Sea on this image taken 20 June 2006. Many of Europe's largest rivers, including the Danube, the Dnister, and the Dnipro (Dnieper) dump fresh water into the sea. The sea's only source of salty water is the narrow Bosporus Strait (in the southwest), which connects it to the Mediterranean Sea through the Sea of Marmara. The diamond-shaped landmass that projects into the sea from the north is Ukraine's Crimean peninsula. Photo courtesy of NASA.