EMPIRE, Mich. -- Early morning dips in North Bar Lake have a profound meaning for Becky Willis.
"It's a whole lot more than just swimming, it's kind of a cleansing," she said.
That daily ritual continued until signs popped up along the little lake's shoreline during the past summer warning of cyanobacteria blooms that could sicken swimmers and harm pets. The first makeshift postings around the lake just north of the town where Willis co-owns an art gallery didn't stop her, but more detailed warning signs with pictures of what to watch for did.
"I looked at a lot of the pictures and it was like, 'Oh yeah, I swam in that,'" she said.
So Willis started swimming in Lake Michigan, although the big lake's chilly water was too much late in the summer when North Bar Lake normally would be more inviting. She had to cut her swimming season short.
"Usually with North Bar I can almost make it into October, the beginning of October, but not this year," she said.
Lake water at the popular tourist spot still was fouled by a type of bloom that has become more common in northern Michigan lakes, and later into the year, according to state Department of Environment, Great Lakes and Energy and local health officials. Climate change could be exacerbating the problems by heating up inland lakes for longer stretches over summer into early fall.
Cyanobacteria blooms are more than just soupy, unsightly messes in lakes. The organism, sometimes called blue-green algae, can produce neurotoxins that cause health problems ranging from itchy skin, runny eyes, asthma-like symptoms, gastrointestinal problems and even death in humans, and problems with pets as well.
That's according to a release from District Health Department No. 10, which in November investigated a bloom in Ryerson Lake near Fremont after the state Department of Health and Human Services received a report.
"I'd say over the last 10 years, and certainly over the last three to four years, we've been getting a lot more algae blooms, it is becoming more common," said department Environmental Health Director Tom Reichard.
There were no reports to the district health department of people or pets having health problems after exposure, from the recent or other blooms within the department's 10-county area, Reichard said. But the timing at Ryerson Lake was unusual, as the last blooms of the season typically are in the first week of October.
"It is probably more than likely related to the fact that we've had a pretty mild winter so far," he said.
Exposure symptoms in people tend to be mild, while dogs may have seizures or die, Reichard said. That's why the health department typically posts warnings on impacted lakes for summer blooms -- no notices were posted at Ryerson Lake, both because the bloom was short-lived and because the water was cold enough to mostly keep people away.
Willis said she had mild stomach issues before she stopped swimming in North Bar Lake, but added there's no way of knowing if the water was the cause. She typically would shower after swimming there and others have told her they avoid it over "swimmer's itch" concerns.
This is the second year in a row cyanobacteria has appeared on several popular northern Michigan lakes, including Au Sable, Black and Cadillac. And for the first time, a bloom was confirmed on Portage Lake in Houghton County -- it's the fourth in the Upper Peninsula in the past three years.
According to data from the Michigan Department of Environment, Great Lakes and Energy, there has been an increase in the number of confirmed cyanobacteria blooms in the state. Aaron Parker, an aquatic biologist with the agency, said more publicity for the blooms has led to a greater number of people reporting them, so that could play a role in the increased number. But he doesn't think that's the only thing going on.
The largest, most notable blooms of blue-green algae in recent years occurred in Lake Erie, and have repeatedly threatened Toledo, Ohio's municipal water supply. During a particularly bad bloom in 2014, the city was forced to shut down it's pumps which draw water from the lake to serve about 400,000 people.
Scientists expect a warming climate to increase cyanobacteria blooms in number and severity. That means they are likely to show up more frequently at higher latitudes. At present, they still mostly occur in the southern part of the state.
But Parker confirmed that he's seeing more of them up north.
"Every year," he said.
He said fall blooms in particular are driven in part by seasonal lake mixing that spreads nutrients throughout the water column, but are dependent on warm spells.
"You'll get these bright, sunny, 70 degree days beating down on this nutrient rich water," he said. "And then you'll just get these ephemeral blooms. They might last a day or two, and then temperatures drop off again, and then they disappear just as fast."
However, a warmer climate isn't the only thing worsening the blooms. Parker said the biggest contributing factor to cyanobacteria blooms is excess nutrient input into lakes.
According to Reichard, septic systems for lakeside homes can be directly feeding the cyanobacteria if sewage is seeping into the surface water.
That could be compounded by people spending more time at lake homes during the pandemic.
He recommended lake home owners have their septic tanks pumped out at least every other year, and regularly inspected.
Shoreline owners should also leave a strip of unmowed vegetation along the lakeshore, to help keep nutrients from running off into the water.
Parker notes that the spread of invasive zebra mussels bolster blooms, too. Their presence in a lake is a competitive advantage for cyanobacteria. The mussels tend to consume other microorganisms.
"Now you'll have this disproportionate population of cyanobacteria that can just take off because they have no other competition now from diatoms or green algae for any resources," Parker said.
No cyanotoxins were found in Grand Traverse County's Long Lake after a bloom prompted testing in October, said county health department Environmental Health Director Dan Thorrel. The county's lakes have largely been bloom-free in recent years, while those in neighboring counties have not, including Leelanau County, he said.
Testing on Aug. 7 confirmed reports of a cyanobacteria bloom in North Bar Lake, said Julie Christian, lead biologist for the National Parks Service at Sleeping Bear Dunes National Lakeshore. The bloom moved around the lake and persisted as late as October, and NPS warned people of the risks.
"We posted signs around the perimeter of the area where people are most likely to get in the water to warn them of the signs," she said, adding the bloom wasn't consistent enough to merit closing the lake to swimming altogether.
Past anecdotes suggest it's not the first bloom in North Bar Lake in the past decade but it's the first documented, Christian said. And volunteer scientists looking for invasive species in Sleeping Bear Dunes' other inland lakes haven't reported cyanobacteria either.
But these blooms are showing up in other national parks, including Pictured Rocks National Lakeshore's inland lakes, so Christian and others with NPS are trying to better understand what's behind these outbreaks, she said.
North Bar Lake doesn't have the shoreline development that could cause nutrient buildup behind other blooms, but it does have invasive quagga mussels, which have their own way of giving the cyanobacteria an advantage, Christian said. She suspects they are filter feeding, then excreting phosphorus.
"Basically the mussels are putting out a whole bunch of fertilizer, and anything that likes the fertilizer is going to grow more robustly, including the bacteria," she said.
Tests showed that cyanobacteria blooms often coincided with times when the lake's outlet into Lake Michigan was blocked, Christian said. That happened frequently during 2020, especially in the fall, and could cause nutrients -- and cyanotoxins -- to build up in the lakewater.
Christian said she hopes to keep studying North Bar Lake, especially its water temperatures, to learn more about what's behind the blooms. Meanwhile, visitors need to look out for blue-green, soupy water or a layer on the surface (Thorrel said it looks more like paint than the fibrous masses algae can form).
Willis is hoping that the blooms don't return to North Bar Lake in 2021 so she can resume her summer morning swims.
"I've got my fingers crossed it'll be back in shape next year, because I so love it, it's my favorite thing to do," she said.