File:Baltic Sea (MODIS 2019-07-28).jpg

English: Spurred by a sweltering heat wave across Europe, swirls of phytoplankton filled the Baltic Sea in late July 2019. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite acquired a true-color image of the colorful scene on July 20.

The Baltic Sea usually experiences two blooms of phytoplankton each year, one in the spring and another in the summer. A fall bloom occurs in some years as well. Phytoplankton are small, plant-like organisms that live in these waters year-round in small numbers. When warm water temperatures, favorable daylight length, and adequate nutrients are present, the organisms can reproduce very quickly to form massive blooms seen from space.

This summer’s Baltic Sea bloom appears to be especially intense. The European Space Agency’s Earth Watching program, the vast algal bloom could post a risk to marine life in the Baltic Sea. According to their website, “The blue-green bloom, which stretches from Finland to parts of Germany and Poland, is the largest the scientist have seen in the Baltic in recent years. They believe a prolonged stretch of warm sea temperatures and a lack of wind, coupled with fertiliser from regional agriculture washing into the Baltic, have caused the bloom.”