This image of the Phytoplankton Blooms in the Black Sea, acquired on May 30, 2006, by the MODIS on the Aqua satellite. It shows swirling blooms of phytoplankton coloring the surface waters blue and green. The large volume of freshwater flowing into the Black Sea from large European rivers. Also including the Danube and Dnieper Rivers, makes the sea much less salty than open oceans.
Therefore freshwater flow also delivers many nutrients, which are washed into the sea from land. Also nutrients support large blooms of phytoplankton: microscopic photosynthetic organisms (algae and bacteria). The chlorophyll and other pigments the organisms use for photosynthesis change the way light reflects off the surface. Therefore these changes are visible in satellite imagery.