Have you ever arrived at the beach and found it carpeted with gunk the colour and texture of Oscar the Grouch? This mucky green substance is Cladophora algae, and it can make a visit to the shore less than ideal.

Cladophora can get tangled around your legs when you wade through the water and saturate waves to such an extent that they sound almost ‘gloppy.’ Fresh Cladophora doesn’t smell too bad, but as it blackens and rots, it gives off a rotten egg smell similar to sewage.

Cladophora algae is icky, but is it harmful to people?


Here are three things you should know about Cladophora algae at the beach:


1. What is Cladophora algae?

Cladophora is a thin, green, hair-like algae that forms in dense mats. Cladophora grows best in shallow, clear, nutrient-enriched water with hard surfaces to attach to (like submerged logs or rocks).

You might find this algae in some of the Great Lakes. In fact, it’s an increasing problem.

Cladophora algae at Cherry Beach, Lake Ontario. Photo by Elise Mackie

It’s been documented in eastern Lake Erie, Lake Ontario, Lake Michigan, and Lake Huron (with small amounts in Georgian Bay and large amounts in the shallow areas of Saginaw Bay).


2. Why is there Cladophora algae in the water or on the beach?

Cladophora blooms happen due to a number of factors. They have been linked to high phosphorus levels in the water which can result from lawn fertilizers, agricultural and urban runoff, and septic and sewage treatment systems.

Invasive zebra and quagga mussels in the Great Lakes are also changing the water in ways that encourage Cladophora growth. By filter feeding, these dreissenid mussels increase water clarity and release particles’ nutrients (like phosphorus) in soluble form. They even provide a hard surface for the algae to grow on—talk about rolling out the red (or rather green) carpet!

Cladophora and zebra mussels at Donner's Point, Lake Michigan. Photo by National Park Service via Great Lakes Environmental Research Laboratory

So, how does the yucky stuff end up between your toes, strung around your kayak paddle, or twisted in your fishing hook? Cladophora algae ends up on the beach when wind and waves dislodge it from what it’s growing on and carry it to shore.

But the real question is…


3. Is Cladophora algae harmful?

Cladophora algae is not toxic like some other types of algae are (such as blue-green algae or red tide). However, Cladophora is considered a nuisance algal bloom and it poses substantial problems for recreation, industry, and wildlife.

Cladophora algae in Lake Erie. Photo by Jessica Gordon

Cladophora algae fouls and stinks up beaches, making water activities like swimming or paddling undesirable. It clogs industrial and municipal water intakes and gets caught in commercial fishing nets, too.

Worse still, before Cladophora blooms spoil your day at the beach, they harm aquatic ecosystems and wildlife. The blooms degrade marine habitats and kill fish by depleting oxygen levels in the water.

Cladophora algae on the shores of Lake Ontario near Ontario Place. Photo by Alysse Mathalon

Although Cladophora algae isn’t dangerous to humans in and of itself, studies suggest that warm, rotting Cladophora incubates E. coli and other bacteria that can be harmful to people. E. coli can make you very sick with vomiting, diarrhea, or less commonly, a serious disease or infection.

Often, crustaceans and other tiny treats wash up to shore along with the Cladophora, enticing gulls from far and wide to feed (then poop) in the area. This causes even higher concentrations of bacteria in the algae and on the beach.

Cladophora? More like Cladophor-NAH.


One thing Cladophora is good for is giving information about water.

The Biodiversity Conservation Strategies of Lake Erie, Lake Michigan, and Lake Ontario all measure Cladophora to learn about ecosystem health, with certain amounts of the algae indicating ‘good’ conditions.

The Lake Erie – Niagara citizen science monitoring hub, which was formed with and hosted by the Niagara Coastal Community Collaborative, conducts regular Cladophora monitoring through two citizen science initiatives every summer.

“While Cladophora doesn’t get quite the attention that harmful algae does, the levels we’re seeing throughout the Great Lakes, particularly in Lake Erie’s eastern basin, is an indicator that something is wrong. Here and elsewhere on the Lakes, we have these beautiful waterfronts that are rendered effectively unusable by the excessive Cladophora washup.”

– Gregary Ford, Niagara Community Monitoring Coordinator

Cladophora algae in Lake Erie. Photo by Jessica Gordon

In the summer of 2020, the Toronto citizen science monitoring hub on Lake Ontario saw increased amounts of Cladophora algae at Ontario Place, Centre Island Beach, and Cherry Beach.

Cladophora algae on Cherry Beach, Lake Ontario. Photo by Elise Mackie

If you see Cladophora algae, you can take a photo of it and report it to your local health authority. Reporting Cladophora when you see it can help us learn more about it.

If you really want to take a stand against Cladophora, you can get involved in Cladophora monitoring to become a citizen scientist. For more information, check out the Lake Erie – Niagara citizen science monitoring hub and the Niagara Coastal Community Collaborative.

Read the Frequently Asked Questions: Lake Erie – Niagara Monitoring Hub here.

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