stylistic:tone, structural:reformatting
Environmental status

Satellite images taken in July 2010 revealed a massive algal bloom covering 377,000 square kilometres (146,000 sq mi) in the Baltic Sea. The area of the bloom extended from Germany and Poland to Finland. Researchers of the phenomenon have indicated that algal blooms have occurred every summer for decades. Fertilizer runoff from surrounding agricultural land has exacerbated the problem and led to increased eutrophication.

Approximately 100,000 km (38,610 sq mi) of the Baltic's seafloor (a quarter of its total area) is a variable dead zone. The more saline (and therefore denser) water remains on the bottom, isolating it from surface waters and the atmosphere. This leads to decreased oxygen concentrations within the zone. It is mainly bacteria that grow in it, digesting organic material and releasing hydrogen sulfide. Because of this large anaerobic zone, the seafloor ecology differs from that of the neighboring Atlantic.

Plans to artificially oxygenate areas of the Baltic that have experienced eutrophication have been proposed by the University of Gothenburg and Inocean AB. The proposal intends to use wind-driven pumps to pump oxygen-rich surface water to a depth of around 130 m.

After World War II, Germany had to be disarmed and large quantities of ammunition stockpiles were disposed directly into the Baltic Sea and the North Sea. Environmental experts and marine biologists warn that these ammunition dumps pose an environmental threat with potentially life-threatening consequences to the health and safety of humans on the coastlines of these seas.

Climate change, pollution from agriculture and forestry, impose such strong effects on the ecosystems of the Baltic sea, that there is a concern the sea will turn from a carbon sink to a source of CO2 and methane.