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A bird flight from American rivers shows that about 1 in 3 have changed color in the last three decades, reports WordsSideKick.com. They have specifically gone from blue to yellow or green shades since 1984, according to a comprehensive analysis of satellite images set out in a new study. Researchers do not present it as a doom and gloom report because there are so many variables involved, but they say that their relatively simple measure can be another tool to measure waterway health. In general, rivers turn yellow due to excess sediment and green due to excess algae, while blue indicates ‘clean, healthy water systems’ per Smithsonian. According to the new report, which analyzed more than 235,000 images from 1984 to 2018, more than half of the U.S. rivers were yellow, about a third were green and 8% were blue. See this interactive map.
“Most rivers change gradually and are not noticeable to the human eye,” lead author John Gardner of the University of North Carolina tells Live Science. “But areas that change the fastest are more likely to be man-made.” Think of dams, reservoirs and increased development, all of which could alter the “nutrient flow” in the rivers, says a scientist from the University Corporation for Atmospheric Research. A professor of atmospheric science at Penn State adds that climate change may also be a factor because warmer temperatures will usually increase algae. Yet I do not believe there are immediate threats to human health due to the shift in colors, Gardner says. Although rivers can change color seasonally due to factors such as snow, the 1-in-3 figure melts into rivers that have undergone long-term shifts. (Read more river stories.)