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What's that slimy stuff on the bottom of the lake? Golden brown algae

Golden brown algae along the bottom of Torch Lake. (Photo: Torch Conservation Center)
Golden brown algae along the bottom of Torch Lake. (Photo: Torch Conservation Center)

Golden brown algae first made headlines in 2014 when aerial photos showed it coating the bottom of typically turquoise Torch Lake.

Since then, homeowners and lakegoers have noticed the algae covering the bottoms of other lakes throughout northern Michigan and the U.P., often in zebra-like stripes.

“We know currently there's no health hazard to humans, or nonhumans. It’s just really ugly and slimy,” said Samantha Ogle, a lake biologist.

Ogle says the algae is usually its densest this time of year, after a season of soaking up sunlight and nutrients.

“If you can imagine a mossy forest floor, it’s kind of like that, but in the water and it’s golden brown,” said Ogle. “Depending on the … ecology of the lake where it's growing, sometimes it'll look really, really brown. Other times it looks [like a] more bright, goldy color."

Ogle says it’s not toxic, not invasive, and not aesthetically pleasing, but beyond that, there’s a lot we don’t know about the algae.

“We don't fully understand why it is here, why it is suddenly exploding in the past few years,” she said. “There's a lot of theories around what is happening, but there is a lot that we don't know yet.”

One theory is that Dreissenid mussels, like Quagga and zebra mussels, are cleaning the water by sucking up plankton. That clearer water allows sunlight to penetrate deeper and warms the water column, creating better conditions for plant growth.

Another idea is that increased nutrients in groundwater and runoff are contributing to algae growth. Others think disease may have killed the algae's main herbivores, allowing it to grow.

But Ogle says that because there isn’t a health concern, bigger agencies at the state and federal level aren’t dedicating as many resources to researching the uptick in golden brown algae growth.

But lake associations in the area, like the Three Lakes Association in Bellaire, have funded their own research on the issue. And some of those research efforts are just recently picking up steam with the help of federal scientists.

Ogle says even though the algae isn’t harmful to humans, it could be an indicator about lake health in northern Michigan.

“Our water is kind of what draws people here," she said. "So we need to protect it and understand what's happening. Like, are the lakes trying to tell us something? Or is this just kind of a new change for us?”

Golden brown algae, like many other kinds of algae, is formed by diatoms: small, single-celled organisms that grow together under the right conditions.

They’re often particular about the conditions they grow in. Ogle says that in itself could tell us something about the health of our waters and the recent explosion in golden brown algae.

“Our lakes are living, breathing ecosystems. So there has to be this huge food chain, and these guys are at the bottom. These guys are here for a reason. We just don't fully understand why yet.”

She hopes more research will bring more answers.

Ellie Katz joined IPR in June 2023. She reports on science, conservation, and the environment.