The Greek philosopher Heraclitus once said "You cannot step in the same river twice," and a recent study done by CSU shows why.

Researchers from Colorado State University, the University of North Carolina at Chapel Hill and the University of Pittsburgh teamed up to study how rivers have changed over the years. The group of scientists analyzed more than 15.9 million satellite images that were taken throughout the past three decades, all focusing on rivers across the country.

The data showed that in the last 36 years, approximately one out of every three large American rivers has significantly changed color. Rather than seasonal changes, these are long-term color shifts, where rivers are permanently turning green, red and yellow.

While they can't 100% back the claim, the team of researchers told Salon.com, they don't currently think the color changes in America's rivers have negative impacts on the health of humans.

Human activities, however, are believed to have an effect on certain rivers changing hues. Scientists say that factors like man-made global warming and increased urbanization interfere with how rivers receive their nutrients. Suspended sediment, increased algae and a decrease in nutrients and light result in rivers changing color over time.

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