If you guessed algae, you're right.

New research published in Communications Earth & Environment suggests algae growth is increasing in Canada's lakes — even remote ones — and climate change is the main culprit.

A team led by researchers at McGill University in Montreal and Université Laval analyzed sediment cores taken from 80 lakes across the country and found that algae has been increasing in the majority of them since the mid-1800s.

For lead author Hamid Ghanbari, the most interesting finding was a spike in the rate of the increase in algal growth: since the 1960s, it increased sevenfold.

"This was something very surprising for us and when we compared our data with other historical records, we found out that rising temperature is a major factor," Ghanbari said.

Aside from climate change, excess nitrogen and phosphorus can also contribute to algal growth when they are carried into waterways through runoff from animal manure and chemical fertilizers, stormwater and wastewater.

Algae, along with bacteria and phytoplankton, are essential for the aquatic food web. But too much algae can be a bad thing. 

The recently published peer-reviewed study looked at algal growth overall and didn't analyze for blooms.

While some lakes see some algae as a part of their cycle, Ghanbari said the concern is what will happen if the increase in algae leads to growth outside of what's normal.

"That's where the problem starts," he said. "We don't know at the moment what that threshold is, but we know the increasing chlorophyll or algae levels in the lakes could lead to several problems."

Ghanbari said excess algae growth can harm aquatic life and even human health — reducing water quality, depleting oxygen in the water and creating blooms that can release dangerous toxins, as residents along the shores of Lake Erie know all too well.

Daryl McGoldrick, head of water quality monitoring and surveillance for the Great Lakes for Environment and Climate Change Canada, said while increasing algal growth doesn't necessarily mean more toxic blooms, there is a risk to aquatic life.

"The study is in line with what we see and [what we] suspect are impacts of warming," McGoldrick said.

Global and local action can help

Maëlle Tripon, a project manager with Quebec freshwater advocacy group Fondation Rivières, said her team has noticed first-hand that when it's warmer, they see more algae on lakes. 

She said her takeaway from the research is that tackling algal growth cannot solely rely on local action.

"We already knew we need to change locally — like farming practices and also, for example, we need less paved and waterproof surface in the cities," she said. 

"But what the study shows is that we also need global policies to alleviate climate change."

Ghanbari agreed, but added that individual choices can still help reduce algal growth. 

"Simple acts such as reducing the fertilizers … or properly disposing of household chemicals, these simple acts could really help the lakes," he said.