"Industrial agricultural has significant socioeconomic and environmental costs, although scientists are bringing solutions."

"A musty smell repels swimmers from some Iowa lakes in summer, when the bodies of water too often turn brown, green, or blue-green.

Researcher John Downing says his state is 92 percent cultivated, so fertilizers seep off croplands into waterways during rains, prompting algae blooms that can harm drinking water and make it tough to boat or catch sport fish. Less than half a pinhead of phosphorus per gallon of water-"a phenomenally tiny quantity," said Downing-is enough to turn a lake bright green.

A fleck of phosphorus fertilizer costs a farmer almost nothing. "But that half pinhead per gallon can cost society millions in lost recreational value and cleanup costs," said Downing, an Iowa State University professor whose water-monitoring group tests 137 Iowa lakes.  "We don't have lakes that we could point to and say: 'Here is a pristine lake that has been unimpacted by people.' "  "

Sally Deneen reports for National Geographic News January 23, 2012, as part of a special series on global water issues. [2]