Geographical Research Letters. Some river segments became more red. Only about 5% of U.S. river mileage is considered blue — a color often equated with pristine waters by the general public.
About two-thirds of American rivers are yellow, which signals they have lots of soil in them. But 28% of the rivers are green, which often indicates they are choked with algae.
And researchers found 2% of U.S. rivers over the years shifted from dominantly yellow to distinctly green.“If things are becoming more green, that’s a problem,” said study lead author John Gardner, a University of Pittsburgh geology and environmental sciences professor.