(Newser) – A three-year environmental study has produced a color-coded map of the Great Lakes, with Ontario and Erie clearly under the most stress from a hodgepodge of factors, reports the Detroit Free Press. (See the map here.) One big culprit with those two lakes, however, is fertilizer runoff from farms, says a University of Michigan researcher, citing "some of the heaviest loads of phosphorous in North America."
Lake Superior fares the best in the study, with huge swaths of its water a low-stress blue. Then come lakes Huron and Michigan, with most of the latter falling in the second-highest color range of stress. Factors such as invasive zebra mussels, dwindling ice cover, mining, and even light pollution are taking a toll. Researchers say a comprehensive strategy is required for the entire ecosystem, instead of individual ones that focus on just one high-profile issue at a time (like zebra mussels).