TRAVERSE CITY, MI (AP)-- Scientists say Lake Michigan's Green Bay is developing "dead zones" similar to sections of Lake Erie and the Gulf of Mexico, where there's so little oxygen that few if any organisms can survive.
In a Web presentation Thursday, experts said the primary culprit is excessive levels of nutrients such as phosphorus that wash into the Wisconsin bay from farms, industry and municipal wastewater treatment systems.
The nutrients feed algae that eventually dies and sinks to the bottom, where it decomposes. The process uses large volumes of oxygen.
Tracy Valenta of Green Bay's Metropolitan Sewerage District says phosphorus levels in the bay have jumped in recent years.
She says the oxygen drop-off may explain the disappearance in the area of the burrowing mayfly, a species whose presence indicates a healthy ecosystem.