Blue-green algae alert: How to know when it’s safe to go into the water

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Roll out those lazy, hazy, crazy days of summer, those days of soda and pretzels and blue-green algae?

With apologies to the late, great Nat King Cole, visitors to Meech Lake have been greeted with an eyesore for the past several days: a turquoise-tinted sludge that prompted the National Capital Commission to close popular O’Brien Beach to swimmers for public safety reasons.

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It’s not an entirely new story in these parts. Last July, Ottawa Public Health also advised against water exposure at the Long Island Locks along the Rideau River near Manotick when blue-green algae — technically known as cyanobacteria — appeared on the surface.

The blue-green algae, however, shouldn’t be confused with the nasty-looking, but relatively harmless green scum that settled atop the Rideau Canal in the summer of 2020.

So, what, exactly is blue-green algae?

Cyanobacteria typically shows up in mid to late summer, with large clumps — “or blooms” — appearing on the surface, often looking like a large bowl of pea soup. Yum.

It’s most common in shallow, slow-moving warm water under hot conditions.

What causes the blooms?

Bacteria develops through the photosynthesis process and continues to grow quickly into blooms that float atop the water.

Larissa Holman, director of science and policy for Ottawa Riverkeeper, a charitable organization that promotes protection of the Ottawa River watershed, says it’s early in the season to see the algae develop.

“It comes from the run-off nutrients from the land that are released into waterways,” Holman said. “At certain times of the year, (the blooms) are higher, usually when it’s really hot. They’re usually more commonly seen in late July or August.”

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The blooms, Holman says, are a normal part of ecosystem health and release oxygen.

Over time, though, they can become problematic “when it’s too hot and the blooms hang around too long.”

Rainfall can chase the blooms away. Thursday’s forecast was calling for rain, which could help push away the algae at Meech Lake.

Not all algae is created equal, though, and it’s the blue-green form that is potentially toxic for people and pets.

There’s a murkiness amid the blue-green stew, too. Sometimes it’s toxic, sometimes it’s not.

“The only way it can be confirmed is through testing,” Holman said.

Caution, as was the case with the NCC’s decision at Meech Lake, is the best policy.

What are the potential dangers of blue-green algae?

Small doses of exposure — as little as a mouthful or two — can result in serious health problems, including liver damage.

The most common toxins produced by cyanobacteria are microcystins and anatoxins.

Inhaling microcystins can cause vomiting, diarrhea, blood in stools, jaundice, even seizures and potential liver damage. Anatoxins are related to the nervous system. Exposure could create problems related to muscle tremors and paralysis.

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“It’s best to respect public health messages and generally avoid those areas,” Holman said. “But, if you think you might be exposed, rinse off as quickly as possible.”

What’s the danger for animals?

Dogs are particularly vulnerable, considering that even a slurp or two of infected water can cause problems.

A short swim can be an issue, too, given that an animal licking its paws and skin afterwards can accidentally inhale the toxins.

In 2021, a Doberman puppy in King City, Ont., died after drinking out of a man-made backyard pond that contained blue-green algae.

In 2019, three dogs in Fredericton, N.B., died after being exposed to toxins in the St. John River.

According to the Ontario Veterinarian College, the first course of action for an animal that could be exposed is to rinse with clean water.

A note to those who fish, as well. It’s not recommended to eat fish caught in water with blue-green algae.

What is green algae?

The majesty of the Rideau Canal took a major hit back in 2020, when a lime gunk covered parts of the waterway downtown: a green carpet, of sorts, for those checking out the scenery near the National Arts Centre.

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Conditions were rife for algae growth because it was hot, the canal was narrow with little flow and boat traffic was limited due to COVID-19 pandemic public health measures.

Yet, while that algae bloom — green filamentous algae for the science types out there — looked ugly, it was harmless from a health standpoint.

“It’s totally natural,” Holman said. “It’s a nuisance for paddling and swimming and it’s aesthetically unpleasant and usually keeps people away.”

Ultimately, that scum was removed when the NCC brought in a weed harvester.

Ottawa Public Health advises that residents concerned about possible blue-green algae blooms should contact the Ontario Ministry of the Environment, Conservation and Parks. That agency will follow up and take water samples if necessary to determine whether the water is free from toxins.

kwarren@postmedia.com

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