The number of "dead zones" in the ocean - sites of massive marine life die-offs due to low dissolved oxygen - has increased by 33% since 2004, according to Nick Nutall of the United Nations Environment Programme (UNEP).Growing up to 100,000 square kilometres in size, the dead zones result primarily from nitrogen pollution originating on land, usually from fertilzers and sewage. The nitrogen spurs the growth of algae, which consume all the oxygen in the water. According to Nutall, there were an estimated 150 dead zones in 2004, increasing to about 200 today. The growth of dead zones could accelerate dramatically over the next 50 years as the world's coastal populations rise, said Achim Steiner, executive director of UNEP.
Source: Stephen Leahy, Interpress Service News Agency, October 5. Marine Scientists Report Massive "Dead Zones".
Image Source: CBS News, August 12, 2006. Pacific 'Dead Zone' worse than thought.