National Lakeshore looks for algal blooms on North Bar Lake

Photos courtesy of Chris Otto / Sleeping Bear Dunes National Lakeshore

From staff reports

Chris Otto, a water resources biologist at Sleeping Bear Dunes National Lakeshore, is keeping a close eye on North Bar Lake in late July and early August—often the warmest time of the summer—for greenish algal blooms and signs of cynobacteria at the popular swimming destination.

Last summer National Lakeshore staff observed the first widespread algal bloom on July 22 and 10 times in August, but sometimes sporadically and for short amounts of time. Sleeping Bear Dunes is working with the National Park Service and the U.S. Geological Survey to monitor cynobacteria blooms in 16 parks nationwide.

“They’re highly variable. It will be there at 10 a.m. but it won’t be there at noon,” said Otto. “It’s fascinating to watch, but difficult to manage.”

Algal blooms are damaging to water quality and to fish populations, and they’re on the rise globally as Climate Change drives up temperatures. Cynobacteria blooms also contain toxins that are hazardous to humans.

“If you see blooms, you want to not be in the water touching it,” said Otto. “It’s a significant health and safety concern. Getting it on your skin can cause rashes. Or worse, you can have liver damage or neurological issues.

Otto said that Lakeshore staff don’t entirely know what drives the algal blooms this time of year. But he points to a few likely factors: water temperatures are high in late July and August (the highest temperature recording in 2021 was 25 degrees Celsius, or 77 degrees Fahrenheit); sunlight penetrates deeper into the water, and windy days that dissipate the blooms are less frequent, but hydrological changes may also play a role—62 percent of blooms last year occurred when North Bar’s outlet to Lake Michigan was closed off.

Last year, at the first signs of an algal bloom, Lakeshore staff posted warning signs with information from the Michigan Department of Health and Human Services and left them up through the summer.

“If you see a bloom, stay away from it,” said Otto. “We’re not saying don’t swim in lake, we’re saying avoid the bloom.”