Baltic Sea, 2005 July 13 (From Baltic Sea Portal) - Blue-green algal blooms, which are basically a population explosion of these organisms as a result of increased nutrients in seawater, cover the Baltic. The highest concentrations occur in the Central Baltic and around the island of Gotland. The Bay of Riga is also the site of algal blooms. The blooms are less intense in the Gulf of Finland and in the Archipelago Sea to the east. Near the coast of Finland, surface wind has cleared the waters of algae accumulations. Some species of blue-green algae are toxic to humans and the surveillance of blooms on the surface and in the underlying water masses is an important task to preserve the health and safety of people living along the coasts. Blue-green algae are not really algae at all but a bacteria known as "cyanobacteria". Intensive blooms like the one observed by Envisat were a rare phenomenon a hundred years ago, but have become increasingly frequent in recent years as a result of the increase in temperature in Baltic and Finnish coastal waters, as well as the increase of pollution in these seas which provide ample nutrients for these organisms.

This Medium Resolution Imaging Spectrometer (MERIS) image, acquired on 13 July 2005 over the Baltic Sea, shows a large population of algal blooms (the green area visible in the centre of the image).

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