This past July, a severe bloom of blue-green algae began spreading across the western half of Lake Erie. It eventually grew to 620 square miles.

(NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey)

At a Glance

Algae blooms increased in more than two-thirds of the 71 lakes that were examined.In the U.S., freshwater blooms result in the loss of $4 billion each year.Climate change is likely hampering lake recovery in some areas.

Costly, and potentially toxic, algae blooms have gotten worse over the past 30 years, according to a new study that looked at freshwater lakes around the world.

Climate change may be making efforts to control these blooms more difficult, the study said.

Algae blooms occur when a population of microscopic phytoplankton in a body of water increases rapidly, sometimes because of fertilizer or other nutrients being washed into the lake or river. Some blooms, such as cyanobacteria, release toxins that can sicken or kill animals and people.

In 2018, a bloom of cyanobacteria, also called blue-green algae, and led to the governor declaring a state of emergency. This summer, a toxic grew to 620 square miles, nearly eight times the size of Cleveland.

"Toxic algal blooms affect drinking water supplies, agriculture, fishing, recreation, and tourism," Jeff Ho, the new study's lead author, said . "Studies indicate that just in the United States, freshwater blooms result in the loss of $4 billion each year."

Lake Okeechobee routinely faces algae blooms. Toxic blooms in Florida resulted in states of emergency being declared in 2016 and 2018.

(NASA Earth Observatory image made by Joshua Stevens, using Landsat data from the U.S. Geological Survey)

For the study, , researchers from the Carnegie Institution for Science and NASA pored over three decades of data from NASA and the U.S. Geological Survey's Landsat 5 satellite. They looked for long-term trends in summer algal blooms in 71 large lakes in 33 countries.

"We found that the peak intensity of summertime algal blooms increased in more than two-thirds of lakes but decreased in a statistically significant way in only six of the lakes," Anna Michalak, another of the study's authors, said in the release. "This means that algal blooms really are getting more widespread and more intense, and it's not just that we are paying more attention to them now than we were decades ago."

The study didn't find a reason for the increase in the intensity of blooms. It did, however, find that lakes with a decrease in bloom intensity warmed less compared to other lakes.

"This suggests that climate change is likely already hampering lake recovery in some areas," according to the news release.

Michalak told Gizmodo “is that tackling climate change will also benefit us in many other ways, such as safeguarding water quality.

“A second takeaway,” she said, “is that water management strategies need to take into account the fact that temperatures and rainfall are changing. Doing so will increase the chance of success of those strategies.”