new study published by the American Geophysical Union is the first global survey of lake colors. While this may not seem like an important topic, color is directly tied to the ecological health of a lake and is intimately influenced by the climate. Since the climatehas been changing, so has the algae and sediment content of lake water, shifting the color from blue to brownish.

To be clear, less than a third of all lakes are naturally blue in color. These are mostly deep lakes found in cool, high latitude environments with winter ice cover and high precipitation. Worldwide, 69 percent of lakes are already green-brown.

“No one has ever studied the color of lakes at a global scale,” said Xiao Yang, remote sensing hydrologist at Southern Methodist University. “There were past studies of maybe 200 lakes across the globe, but the scale we’re attempting here is much, much larger in terms of the number of lakes and also the coverage of small lakes. Even though we’re not studying every single lake on Earth, we’re trying to cover a large and representative sample of the lakes we have.”