Phytoplankton blooms in the Black Sea, satellite image. North is at top. Water is blue, vegetation is green. Ice and cloud cover are white. The Black Sea and its northern sub-section the Sea of Azov (upper right) are inland seas situated in southeastern Europe. They are fed by a network of rivers in a catchment area dominated by agricultural land. The waters draining to the seas have a high sediment load and also contain nutrients from fertilizer. This has led to enrichment of the sea water and a subsequent proliferation of phytoplankton (microscopic algae) in the sea. The algal blooms appear as plumes of discoloured water. An increase in phytoplankton can cause a decrease in dissolved oxygen content, which can make the water inhabitable. Image obtained on 22nd May 2004 by the Aqua satellite.