The coastal dead zones result from fertiliser and sewage running off the land and into the seas. But at least 500 dead zones have now been reported near coasts, up from fewer than 50 in 1950. But these dead zones have expanded dramatically, increasing by millions of square kilometres since 1950, roughly equivalent to the area of the European Union. Furthermore, the level of oxygen in all ocean waters is falling, with 2% – 77bn tonnes – being lost since 1950. However, in some places, the algae can lead to more food for fish and increase catches around the dead zones.

Source: The Guardian January 04, 2018 18:56 UTC