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Cyanobacteria (Blue-Green Algae)

blue green algae blooms along the shore

Blue-green algae blooms (known specifically as cyanobacteria or sometimes called “pond scum”) are large masses of a type of bacteria called cyanobacteria and occur naturally. They can be found in oceans and many freshwater lakes, bays and inlets. Harmful Algae Bloom (HAB) is another term to describe blue-green algae, since it can be harmful to people and pets. Know the facts to reduce your risk.

Where and how do Harmful Algae Blooms form?

When conditions are right, HABs can be found in some Ontario waterways (especially where water is shallow, slow moving and warm, especially if the water has been contaminated with fertilizer, sewage or phosphate soap). Normally, algae are barely visible. During warm weather, this can change as algae rapidly increase in size to form large masses called blooms. HABs are usually detected in the hot summer months and early fall, often forming repeatedly in the same lake or waterway.
Dense blue-green algal blooms can make the water look like a bluish-green pea soup, or a shiny paint slick. Although cyanobacteria are often called blue-green algae, blooms can range in colour from green to red. Fresh blue-green algal blooms often smell like fresh cut grass, while older blooms can stink like pig pens or rotting garbage.

What is the risk to people and pets?

While many forms of blue-green algae are harmless, some may produce toxins that can negatively affect health. If you see HABs in a waterway, do not swim, drink or use the water. Keep animals away from the water too. Longer exposure to more severe toxins in the water through drinking, swimming, bathing, cooking or washing may lead to health problems. This includes: itchy, irritated eyes and skin; headache; fever; diarrhea; abdominal pain; nausea; and vomiting. If you have any of these signs or symptoms, see your health care provider.

NOTE: Never boil the water, as it kills the algae resulting in the release of more toxins. If you feel unwell after encountering a HAB, seek medical attention.

What to do if you see Harmful Algae Blooms in the water?

If you spot a bloom, report it to the Spills Action Centre at 1-800-268-6060. If your home or cottage gets its drinking water from a local waterway, consider using test strips to check if algae toxins are present, even if a bloom is not visible.
In general, HABs can be placed in one of three categories depending on how bad they are. In categories two or three, people should not swim or use water at all.

What are the different categories of Harmful Algae Blooms?

Category 1

Category 1 appearance and precautions

Appearance

The water appears cloudy, but you can still see your toes.
Particle density can vary greatly in the water column.

Health precautions

Health effects are unlikely at this stage, but toxins might still be present. Monitor the water quality for decrease in clarity, cloudiness and change in color.
It is unsafe to swim or to allow children to play in water if you cannot see your toes in the water.
Wait until the bloom has subsided and the water is clear.

Drinking water precautions

Consider using test strips to determine if toxin is present in raw water.
If you don't have test strips or suspect a toxin is present, refer to precautions described in categories two and three.

Category 2

body of water with moderate levels of blue green algae blooms

Category 2 appearance and precautions

Appearance

There is a significant change in the cloudiness and colour which may appear blue, green, brown, red, etc.
Algae may be in clusters, balls, or flakes in the water, like pea soup.
Water may have a noticeable taste and smell that can be described as earthy, musty, grassy, or septic

Health precautions

Do not swim in category 2 HABs or in any bloom which obscures your view into the water It is unsafe to swim or to allow children to play in any dense algal bloom, since you cannot see into the water. Wait at least 24 hours after the bloom has disappeared and the water is clear.
Do not allow pets to swim in the water. Pets will lick their fur and could ingest toxin that could make them ill.
In category two blooms individuals may develop mild symptoms of skin rash or eye irritation.
Do not eat organs of fish caught in an area with HABs.

Drinking water precautions

Do not use the water from a category two bloom for drinking, cooking, rinsing fruits or vegetables, washing dishes, or other consumption. Instead, use potable water from a safe alternative source.
Do not boil the water as it kills the algae resulting in the release of more toxins in the water.
Do not let pets or livestock drink the water.
Be observant of when the water has cleared. If you treat surface water for cooking or consumption as per recommendations, wait until after the bloom has disappeared before resuming normal use of the treated water.
Over time, the toxin is naturally reduced by dilution, degradation by other bacteria in the water, and sunlight. If the bloom re-appears, repeat the precautions.

Category 3

body of water with high levels of blue green algae blooms

Category 3 appearance and precautions

Appearance

This is a dense bloom; it may resemble an oil or paint spill and the surface of the water may form a scum.
Water may have a noticeable taste and smell that can be described as earthy, musty, grassy, or septic
Algae is easily swept by the wind and deposited near the shore.

Health precautions

Do not swim in category 3 HABs or in any bloom which obscures your view into the water. It is unsafe to swim or to allow children to play in any dense algal bloom, since you cannot see into the water. Wait at least 24 hours after the bloom has disappeared and the water is clear.
Do not allow pets to swim in the water. Pets will lick their fur and could ingest toxin that could make them ill.
In category two blooms individuals may develop mild symptoms of skin rash or eye irritation.
Do not eat organs of fish caught in an area with HABs.

Drinking water precautions

Do not use the water from a category three bloom for drinking, cooking, rinsing fruits or vegetables, washing dishes, or other consumption. Instead, use potable water from a safe alternative source.
Do not boil the water as it kills the algae resulting in the release of more toxins in the water.
Do not let pets or livestock drink the water.
Be observant of when the water has cleared. If you treat surface water for cooking or consumption as per recommendations, wait until after the bloom has disappeared before resuming normal use of the treated water. Over time, the toxin is naturally reduced by dilution, degradation by other bacteria in the water, and sunlight. If the bloom re-appears, repeat the precautions.

How to further protect your drinking water from Harmful Algae Blooms

If you get drinking water from a lake, river, creek or a shallow well near a body of water, ensure the water is properly treated to protect against harmful bacteria and HABs. Water treatment is a complex process. Consult a qualified professional who can assess your water supply to ensure the best treatment system is in place. If unsure about the effectiveness of your water treatment system, find another source of drinking water such as a drilled well, a dug well far from shore, or water holding tank filled with water from a licensed water treatment plant. An alternate water source may also be recommended if you draw water from a water source that has frequent HABs.
Do not drink water that is contaminated with cyanobacteria. If you obtain water from a surface water source that might be contaminated with cyanobacteria, contact the Ontario Ministry of the Environment’s Spills Action Centre at 1-800-268-6060 or 416-325-3000. Conventional water treatment and boiling are not effective at removing cyanobacterial toxins.

Are there water treatment systems that reduce toxin levels from Harmful Algae Blooms?

Yes. Water treatment systems based on the following technologies can reduce cyanobacteria toxin levels:
- One micron filter, cleaned or replaced frequently (as per manufacturer’s instructions), for removal of cyanobacteria cells, PLUS
- Reverse osmosis, PLUS
- Ozonation, or chlorination (with adequate levels and contact time), PLUS
- Point-of-use filter (installed on a specific tap) that has been certified to NSF/ANSI 53 f or microcystin reduction.
KFL&A Public Health recommends property owners consult a qualified water quality specialist about appropriate water treatment equipment capable of reducing cyanobacteria toxin levels.

What can be done to prevent Harmful Algae Blooms?

Human activities (like fertilizer runoff, agricultural runoff and faulty septic systems) can increase levels of phosphorus and nitrogen in the water. This can lead to the growth of HABs. To reduce the nutrient levels in water that promote algae growth, do the following:
- Use phosphate-free laundry detergents.
- Avoid using fertilizers.
- Reduce surface runoff by maintaining a naturalized shoreline on waterfront properties.
- Ensure septic systems work properly and are maintained so sewage does not leak.

Resources

Blue-Green Algae (cyanobacteria) and their Toxins - Health Canada
Blue-green algae: Information for cottagers and home owners (PDF) - Ontario Ministry of the Environment
Blue-green algae - Province of Ontario
Guidelines for Canadian Drinking Water Quality - Cyanobacterial Toxins (PDF) - Health Canada