The blooms of toxic blue-green algae on lakes and other freshwater bodies that are becoming a regular fixture of the summer are projected to become a bigger problem as climate change continues to heat things up.

The toxic algae, known as cyanobacteria, thrive in warmer conditions and when there are excessive nutrients in the water. A new study about this was published online in June and in print last week by scientists at Tufts, MIT and other institutions in the journal “Environmental Science & Technology.”

Lead author Steven Chapra of Tufts said the researchers expected the greatest impact to happen in the South because of warmer temperatures there. “But, interestingly, the largest effect is found in the northeast,” he said. Chapra said that’s because the models also include the impact of an increase of nutrients like nitrogen in the water. Those levels tend to go up in water bodies with a growth in population and industry. “The northeast has more of those factors that makes things worse,” he said. “And so, at least relatively speaking, it winds up being the biggest.”

Ingestion of the toxins in cyanobacteria can result in neurological damage, liver damage, gastrointestinal problems, irritation of eyes, ears and skin, and other health problems.

"It is estimated that lakes and reservoirs that serve as sources of drinking water for 30-48 million Americans may be periodically contaminated by algal toxins," the authors write in the paper. The paper says drinking water treatment can reduce algal toxins, but removal can sometimes be as low as 60 percent effective. 

The following maps, created for WGBH News by the scientists, illustrate how cyanobacteria concentrations are projected to increase nationally and in the northeast by 2050 and by 2090, based on a more pessimistic view of our ability to reduce emissions (RCP8.5).

Courtesy of Steven Chapra, Tufts University

Chapra said cyanobacteria blooms will become increasingly obvious in the late summer. Places where you can swim now, you will not be able to swim in August [in the future], for example, because you'll have scums on the water," he said.

The study averaged the findings of several different computer models of the climate, including models that considered greenhouse gas emissions, precipitation, water quality and other factors. It also provided estimates based on two different possible climate futures – depending on what happens with levels of greenhouse gas emissions.

The following chart shows how the study projects cyanobacteria concentrations will change over the calendar year in the northeast. For comparison, the black line at the bottom shows what concentrations would be if there were no climate change. But the green, dotted lines illustrate different climate models of how the algae blooms would spike during the summer under what Chapra called the "best we can hope for" with regard to greenhouse gas emissions. The brown lines show the estimates of different models if things are notably worse with those emissions.

Courtesy of Steven Chapra, Tufts University

“It's going to be a very different world in terms of the freshwater environment,” Chapra said. When he grew up going to the White Mountains in the 1950s, Chapra said, the water was pristine. “I learned how to be a trout fisherman because there were a lot of trout around this region,” he said. “That will not be the case in the future.”

Cyanobacteria can lead to areas at the bottom of water bodies where there is no oxygen, killing off ecosystems there. The study says the largest economic impact from algal blooms will be felt in recreation areas in the southeast. Chapra said the study offers policymakers a framework to plan for the future.