But the outbreak may have been more than a sign of the immediate effects of polluted runoff. It could be a warning of what's in store for the region as climate change leads to warmer, more frequent and more intense storms, scientists say.
The 2011 algae bloom in western Lake Erie was the largest on record for the region, and its coverage of 1,930 square kilometers was more than double its average size for the years 1997 to 2010, according to a 2016 scientific paper. The amount of algae in the water was more than seven times higher than in the previous record year.
The algae was the microscopic cyanobacterium _Microcystis aeruginosa_. When it blooms, it can create a floating green slime that can clog water filters, release harmful toxins into the air and water, and foul beaches.
The 2011 bloom, which cost an estimated $1 billion, took place in August after weeks of heavy rainfall that was linked to a weather phenomenon known as a "La Niña." According to the paper's authors, this extreme weather event can lead to above-average precipitation in the Western Lake Erie Basin.
A series of storms dropped 12 inches of rain in 10 days, causing combined sewage and animal waste to run off into rivers, streams and drainage ditches and eventually Lake Erie.
In 2014, a separate study examined climate-related factors that could have contributed to the massive algae bloom.
Researchers found that the record rainfall combined with changes in the wind and the timing of spring warming in the lake led to the right conditions for a cyanobacterial bloom to occur.
"Based on these findings, we expect more severe harmful algal blooms as the climate continues to change in this region," the study concluded.
The 2011 outbreak was a "turning point" in raising awareness of the issue, said Jeffrey Reutter, director of the Ohio Sea Grant College Program at Ohio State University. "A lot of progress has been made since then on the science side of things. We know a lot more and can do a better job of predicting blooms," Reutter said. "But we still need progress on actually stopping them."
There are signs that the problem is getting worse. In July, a bloom was spotted off the coast of Sandusky, Ohio, that covered an area of more than 600 square miles — the largest such bloom in Lake Erie since 2019, according to the National Oceanic and Atmospheric Administration.
In August, satellite imagery revealed a new algal bloom in the Detroit River. The bloom was made up of a type of cyanobacteria called _Dolichospermum lemmermannii_ and covered an area of about 11 square miles.
In an interview, Reutter said the region is already "locked in" for more frequent and widespread algal blooms. "That's a future we have to plan for," he said.
