Researchers say the number of "dead zones" in the world's oceans and coastal areas has nearly doubled every decade since 1960s, to some 400, due mainly to fertilizer runoff.
The World Watch Institute, 2009 State of the World: Into a Warming World (Print Publication). A Worldwatch Institute Report on Progress Toward a Sustainable Society. ed. Linda Starke. Published by W.W. Norton & Company in New York, NY. page xxv.