ST. PAUL, Minn. (AP) _ A study has found that the Great Lakes of Huron and
Michigan have surpassed Lake Superior in water clarity.

Scientists analyzed satellite images from 1998 to 2012 and found that the depth light could penetrate into the water increased by about 20 percent.

Scientists say less phosphorous runoff, climate change and an increase in
invasive zebra and quagga mussels have contributed to the change.

Michigan Technological University Senior Research Scientist Gary Fahnenstiel co-authored the study. He says the mussels filter the water by eating plankton, which absorb light.

Michigan Tech Research Institute Co-director Robert Shuchman also co-authored
the study. He says the decrease in plankton could cause major changes to the ecology in the lakes.