It is also likely that the lake's tributaries host dormant algae cells that can proliferate in the right conditions in Lake Superior.
"One year it's one thing, another year it's something else driving the blooms," Reinl said. "There are a lot of pieces to this puzzle, but this year is following the pattern."
To prevent blooms, Reinl said making shorelines resilient against destructive storms can help keep runoff minimal. Keeping temperatures lower is also vital.
"How are we supposed to affect global, regional air temperatures?" she said. "Doing those things that limit your carbon footprint and contributions to greenhouse gases. We shouldn't overlook that."
On Wednesday, the surface temperature of western Lake Superior was in the mid-60s, several degrees warmer than is typical for this time of year, according to satellite data from the National Oceanic and Atmospheric Administration that stretches back to 2007.
Most recorded blooms on Lake Superior occur earlier in the summer, though other waters can still produce them.
"Blooms may occur through early fall, especially in inland lakes, so people should continue to keep an eye out for bloom conditions before recreating," LaLiberte said. "More concentrated cyanobacterial blooms in inland Minnesota and Wisconsin lakes may resemble spilled paint, opaque 'pea soup,' or black or vividly colored floating mats."
Contact with algae blooms should be avoided; report sightings to firstname.lastname@example.org or email@example.com.©2021 StarTribune. Visit startribune.com. Distributed by Tribune Content Agency, LLC.