This algae bloom off the Coast of Estonia was captured by NASA’s Landsat 7 satellite at 30 meter resolution, on July 16th, 2002. This algae, a type of cyanobacteria, can be found in almost every terrestrial and aquatic habitat - but with the right conditions can bloom and be seen from space as blue-green patches that swirl following surface currents. Lines cutting across the image are the traces of ships.
This is a simple example of real time environmental monitoring using satellites. Factors that lead to these blooms include low winds, increasing temperatures, and nutrients such as phosphorus (often byproducts of fertilizer runoff along the rivers). The Baltic Sea, pictured above, is seeing an increased threat in the last years. These blooms can be toxic and create dead sea zones, and are often monitored from air and space.