Beach Closures and Blue-Green Algae

Nothing’s better on a hot summer day than spending time at your local beach, but warmer temperatures increase the risk of blue-green algae blooms which could lead to beach closures. But what are blue-green algae? Where do blooms come from and how could this affect the swim season?

What is blue-green algae, really? Is it dangerous? 

Blue-green algae, also known as cyanobacteria, are microscopic phytoplankton found in all natural bodies of water. While commonly grouped with algae, cyanobacteria are actually photosynthetic bacteria (bacteria that get their energy from the sun). Cyanobacteria thrive in slow moving or still waters with high nutrient concentrations, particularly when temperatures are high.

Photo: National Capital Commission (NCC)

While most cyanobacteria pose little threat, a number of species can produce toxins, which can cause serious health effects in humans and animals. Toxins are generally released as the cyanobacterial cell dies and breaks down following a bloom event. The most commonly occurring toxin is microcystin, a hepatotoxin that affects liver function. Species such as Microcystis and Dolichospermum (previously called Anabaena) are found in lakes and rivers in our watershed and are capable of producing microcystin. However, as toxins are only released during bloom events and not every bloom produces toxins, the threat of exposure to microcystin is minimal. 

Even if toxins are not produced, blue-green algae blooms can be aesthetically displeasing. Not only are they unsightly, but they can also produce unpleasant odours. Outside of this, blooms can also have a negative effect on the rest of the local ecosystems by blocking sunlight from other phytoplankton and aquatic plant species, depleting oxygen levels and causing localized warming of surrounding water.   

What does blue-green algae look like? How can I identify a bloom?

Under non-bloom conditions blue-green algae generally aren’t visible, it is only when bloom conditions present that they become apparent. A blue-green algae bloom may turn the water surface bluish-green, green (like pea soup) or turquoise. 

Photo: National Capital Commission (NCC)

If you come across what you suspect to be a blue-green algae bloom you can report it to:

In Ontario: Ontario’s Spills Action Centre

In Quebec: Regional Office of the Ministry of the Environment and the Fight Against Climate Change (MELCC)

What causes cyanobacterial blooms? 

Cyanobacterial blooms occur naturally given the right environmental conditions. These include warmer ambient air and water temperatures (usually around 25 degrees Celsius and higher) and increased nutrient inputs. Research has shown that increases in phosphorus in freshwater systems are correlated with increased numbers of bloom events. It’s a complex phenomenon with several factors at play such as: increased rainfall, climate change, increased UV rays as a result of a thinning ozone layer, and variations in the intensity of zooplankton grazing.

Blooms can occur in lakes where the overall health is good or where the average concentration of nutrients is not excessive. For example the June 2019 blooms that occurred in some Gatineau Park lakes. These blooms were preceded by the Spring 2019 flooding which may have temporarily increased nutrient loads in the water. These blooms disappeared quickly and naturally as a result of wind and current action.

Though blooms in the Ottawa River watershed occur more commonly during the late summer (July – September), blooms can occur anytime the right conditions are present. Peak bloom season is generally between late May and early October. 

Are blooms caused by humans?

Although blue-green algae blooms are a natural phenomenon, the frequency and intensity of these bloom events has been increasing, and blooms are now being reported in water bodies not previously known to support bloom formation. This increase has largely been attributed to increases in global temperatures as a result of climate change, as well as increased nutrient inputs as a result of pollution in the watershed and stormwater and/or agricultural runoff. Human activities can have an effect on all of these factors.

Is this something we should expect to see more of in the years to come? 

It’s difficult to predict the occurrence of cyanobacterial blooms as a number of factors contribute to their formation. However, given the increased nutrient loads in water bodies throughout the watershed as a result of the Spring 2019 flooding, it is possible that we will see more blooms throughout the watershed this summer. 

How can there be a bloom of blue-green algae at one end of a lake, while the other end of the lake is rated excellent for swimming?

These differences can likely be explained by the local topography, currents and drainage patterns of the lake. Nutrients and other material that may accumulate in the lake can be drawn by the current towards one beach in particular.        

What happens if I’m exposed to a blue-green algae bloom? 

If you come across a blue-green algae bloom or what you suspect to be a bloom do not enter the water. Keep children and pets away from the water and do not consume any water (boiling water will not remove toxins).

Photo: National Capital Commission (NCC)

Exposure to blue green algae can lead to headaches, nausea, fevers, sore throats, dizziness, stomach cramps/abdominal pain, diarrhea, vomiting, muscle aches, and ulcers on the mouth and lips if ingested as well as skin rashes and irritations to eyes and ears following recreational water use.  

If you do come in contact with a blue-green algae bloom, rinse off your body and see your healthcare provider, especially if you experience any of the symptoms above.

How is a bloom of blue-green algae confirmed? What criteria are used to determine if it’s safe to reopen a beach?

In Quebec, public beach operators must follow the guidelines of the Ministry of the Environment and the Fight Against Climate Change (MELCC) and quickly report any potential cyanobacterial blooms. Photographs of the site are taken, including photographs of samples in glass bottles. These are sent to the MELCC to confirm the observation. If a Category 2 bloom is observed (as defined by the MELCC), the beach is closed and reopened only when all conditions for safe swimming are met.

Under certain circumstances the MELCC may decide to send an expert to conduct sampling for cyanobacteria.  Samples and pictures of bloom materials may also be sent to cyanobacteria experts at the University of Ottawa who can identify the species present.

Following closure, the lake continues to be monitored daily until the bloom has disappeared.

For example, the National Capital Commission (NCC) provides training to their lifeguards so that they can confidently identify blue-green algae blooms and differentiate them from pollen scum which can look like a bloom to the untrained eye. The lifeguards do daily observations and in the rare cases where a bloom is suspected the NCC is notified. 

What are the thresholds? I’ve heard from some people that in Ontario the beach wouldn’t close for this reason. Is that true? Are the regs different? 

The Government of Canada has developed recreational water quality standards of ≤ 0.02 mg/L for total microcystins and ≤100,000 cells/mL total cyanobacteria. However, the MELCC has a more strict guideline which is used for water bodies in their jurisdiction of 20,000 cells/mL total cyanobacteria. As Ontario does not have it’s own recreational water quality standard for cyanobacteria it defaults to the Canada wide standard.

It should be noted that in Quebec, MELCC guidelines are based on visual monitoring in the majority of cases. These guidelines differ according to whether the bloom is Category 1 (low particle density) or Category 2 (medium or high density), depending on visual monitoring.

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