This image, although it seems a painting, it’s an Earth Observation image  from Copernicus Sentinel-2 mission. It shows green algae blooms swirling around the Baltic Sea. We can see algae blooms east of the central Baltic island Gotland – the island on the left side of the image.
‘Algae bloom’ is the term used to describe the rapid multiplying of phytoplankton – microscopic marine plants that drift on or near the surface of the sea. These plants are so small that up to one million can fit in a tea spoon of sea water. So how come we can see them from Space?
Phytoplankton absorb energy from the Sun and nutrients from the water to produce their own nourishment or energy, just like plants on land! This process is called photosynthesis and one of its side effects is that surrounding water is tinted – in this case green. This effect can be detected from space with dedicated “ocean colour” sensors on board satellites.  High water temperatures and sunny, calm weather often lead to large blooms. The bacteria that consume the decaying algae suck oxygen out of the water, creating dead zones where fish cannot survive.  Although algal blooms are a natural part of life in the sea, human activity and the rising of ocean temperatures, due to a warmer climate, are said to increase the number of annual blooms. These can have an impact in tourism and also restrict our diets.