This Envisat image features a phytoplankton bloom in the Bay of Biscay. The bay, an inlet of the North Atlantic Ocean, is bordered on the east by France’s west coast (visible) and on the south by Spain’s north coast (visible). The bay is decorated by blue and green swirls of phytoplankton, microscopic marine plants that drift on or near the surface of the sea. Although some types of phytoplankton are individually microscopic, the chlorophyll they use for photosynthesis collectively tints the colour of the surrounding ocean waters. This provides the means of detecting these tiny organisms from space with dedicated 'ocean colour' sensors, such as Envisat's Medium Resolution Imaging Spectrometer (MERIS) instrument. MERIS acquired this image on 13 April 2009 while working in Full Resolution mode to provide a spatial resolution of 300 m.