Climate change could turn the world’s lakes blue

The brilliant blue color reflected on the surface of the lakes could lose its hue as a result of climate change. These bodies of water are at risk of turning green and brown colors.

A study, published in Geophysical Research Letters, explains that the imminent change in the colors of the lakes would indicate a decline in the state of ecosystem health. Well, although algae and sediments are also responsible for the color, it has been shown that the temperature, precipitation and depth of the lake affect the hue.

About 5 million satellite images reviewed for the study showed 85,360 lakes and water reservoirs around the world between 2013 and 2020. “No one has ever studied the color of lakes on a global scale,” said Xiao Yang, a hydrologist at remote sensing from Southern Methodist University and author of the study.

“There have been previous studies of maybe 200 lakes around the world, but the scale that we’re trying here is much, much larger in terms of the number of lakes and also the coverage of small lakes. Although we are not studying every single lake on Earth, we are trying to cover a large and representative sample of the lakes that we have,” he added.

According to the research, blue lakes account for less than a third of all water bodies and are found in cold, high-latitude regions with high rainfall and winter ice cover. On the other hand, greenish and brown lakes tend to predominate in dry and coastal regions, representing 69% of all lakes.

An interactive map developed by the authors demonstrates the results of the research.

Temperature is an important factor in the hue of the lakes. Climate change may decrease the percentage of blue lakes, many of which are found in the Rocky Mountains, northeastern Canada, northern Europe, and New Zealand.

“Warmer water, which produces more algae blooms, will tend to change the colors of lakes toward green,” said Catherine O’Reilly, an aquatic ecologist at Illinois State University and an author on the new study. “There are many examples of people actually seeing this happen when they studied an individual lake,” she explained.

“Water color is a simple but viable metric for water quality that can be seen from satellites on a global scale,” the study mentions. “If you are using lakes for fishing, livelihoods, or drinking water, the changes in water quality that are likely to occur as lakes become greener may mean that it will be more expensive to treat that water,” the ecologist said.

“There may be periods where the water is not usable and fish species are no longer around, so we won’t get essentially the same ecosystem services from those lakes when they go from blue to green.”

Changes in water color can also have negative consequences on recreational and cultural activities in places like Sweden and Finland, where lakes are culturally prevalent, the research explained. As warming continues, northern European lakes are likely to lose their winter ice cover, which could affect winter and cultural activities.

“Nobody wants to go swimming in a green lake,” O’Reilly said, “so aesthetically, some of the lakes that we always thought of as refuge or spiritual places, those places might be disappearing as the color changes.”