Algae are microscopic plants that naturally live in freshwater and saltwater environments.  Algae can grow quickly during the summer and form a larger growth called a bloom. Some types of blue-green blooms (cyanobacteria), produce toxins. When these blooms die and decay, the toxins may be released into the water and pose health concerns. 

Risk Advisories

It is very difficult to predict if blooms will form.  It is even more difficult to predict if blooms will release toxins.  Blooms of algae and blue-green algae may vary considerably in colour, consistency and overall appearance.  The presence of blooms triggers monitoring since toxins are only formed if there are blooms.

A risk advisory is issued when an algae bloom is observed.  Initial testing is done to confirm if there is cyanobacteria in the algae bloom and the type of cyanobacteria present, if any.  Certain cyanobacteria are toxin producing and others are not.    

• If there is no risk for toxin production, the risk advisory will be lifted and no further testing is required.
• If there is a risk for toxin production, the risk advisory remains in effect.  Visual bloom monitoring will continue until blooms have disappeared and remain absent for 7 days.  At that time, water samples will be tested for toxins.  The risk advisory will be lifted if toxins are within safe limits.  If the toxin levels are above safe limits, then the risk advisory will remain in effect until later test results reveal that they are within safe limits (below current guideline values).

A bloom can appear as surface scum, foam or a mat and/or discoloured water and can be blue, blue-green, green, red, brown or yellow in colour. Some look like paint streaks on the water, while others many not affect the look of the water. The municipality asks anyone who observes water conditions with these characteristics to call 311.

Staff monitors and reports on the status of 19 beaches across the municipality. 

If a beach is closed, do not swim or engage in any other recreational activity that may involve contact with water (e.g., paddling). Keep children and pets away from the water. Do not drink the lake water and please note that boiling water will not remove toxins.

We encourage everyone to follow beach rules and restrictions to be safe when visiting the beaches.

Questions and Answers

What are blue-green algae (cyanobacteria)?

Blue-green algae, also known as cyanobacteria, are plant-like bacterial organisms naturally found in many types of water systems including ponds, lakes, rivers and wetlands. They are not normally visible, but under the right conditions (warm, slow moving, shallow water and enough sunlight and nutrients), blue-green algae are capable of forming blooms. Some types of blue-green algae produce toxins which can be poisonous to humans and animals.

What is a blue-green algal bloom?

Under the right conditions blue-green algae can increase in numbers quickly forming a bloom. A bloom can appear as surface scum, foam or a mat and/or discoloured water and can be blue, blue-green, green, red, brown or yellow in colour. Some look like paint streaks on the water, while others many not affect the look of the water. Blue-green algae toxins have the ability to reach high levels in blooms, which can be harmful to the health of humans and animals. 

Fresh blooms smell like newly mown grass; older blooms smell like rotting garbage. 

When do blue-green algal blooms usually happen?

Blooms in Halifax usually occur in the summer and early fall, but may develop at other times of the year.

What causes a blue-green algae bloom?

Some conditions important for bloom growth include: 

• Warmer water temperatures
• Amount of light and length of daylight
• Wind and water currents (blooms often occur in slow moving shallow water) 
• Excess nutrients (phosphorous/nitrogen)
• Suitable pH

What should I do if I see a blue-green algae bloom? 

Do not swim or engage in any other recreational activity that may involve contact with water (e.g., paddling) in areas where there is a bloom. Keep children and pets away. Do not drink the lake water. NOTE: Boiling water will not remove toxins. 

What happens if you swim in water contaminated with blue-green algal toxins?

If you swim in contaminated water, your eyes and skin may get itchy and irritated. You may also get other hay fever-like allergy symptoms. Skin contact with blue-green algae toxins may cause result in hives, rashes, blisters, etc.  You should wash as soon as possible after contact with the water.

What happens if you drink water contaminated with blue-green algal toxins?

People or animals that drink contaminated water are at risk of headaches, fever, diarrhea, vomiting, cramps, muscle, joint pain, and liver damage.  Symptoms from exposure to blue-green algae toxins can last for several days. Children and immuno-compromised individuals are at a higher risk for the more severe effects. 

What should I do if I come into contact with water contaminated with blue-green algal toxins? 

If you think you might have come into contact with blue-green algal toxins in the water, you should remove any affected clothing and wash with clean water as soon as possible. If you experience symptoms or health effects after recreational contact with affected water, please seek medical advice. 

How harmful are blue-green algal toxins? 

Very few incidents of human poisoning have been reported. People don't usually drink water contaminated with blue-green algae because of the scum and smell.  During recreational activities such as swimming, contaminated water could accidentally be swallowed.

If people are exposed to low levels of toxins for long periods of time, it can potentially have long-term or reoccurring effects in humans. Children are at greater risk than adults of developing serious liver damage should they ingest high levels of toxins, mostly because of their comparatively lower body weight. 

Can I still drink my tap water during a blue-green algae bloom? 

You should not drink water if the waterbody has blue-green algae blooms.  Since toxic blooms cannot be identified sight and need to be tested, it should be assumed that toxins are present.  If you receive your drinking water directly from a source that has blue-green algae bloom, do not drink it even if you have a water treatment system.  Residential water treatment systems cannot remove blue-green algae toxins from the drinking water. 

If you are connected to a municipal or registered water supply, you can continue to use the water as normal unless notified otherwise by the system owner/ operator. If you have your own groundwater well supply, you can continue to drink the water as normal. 

Can I cook using water with blue-green algae in it? 

No. Boiling water does not remove toxins from the water. 

Can I use water contaminated with blue-green algal toxins for washing? 

If a safe source of water is available, don't use contaminated water for washing clothes or dishes. If no alternative safe source of water is available then you may use contaminated water for washing. Exercise caution while doing so by using rubber gloves to avoid direct contact with the water. 

Bathing or showering in contaminated water should be avoided, as skin contact with the toxins can lead to skin irritation and rashes. 

Can I eat fish from water contaminated with algal toxins? 

Toxins can accumulate in the tissues of fish, particularly in the internal organs (liver, kidney, etc.). Levels in the tissues depend upon the severity of the bloom in the area where the fish are caught or collected. Caution should be taken when considering the consumption of fish caught in areas where blue-green algal blooms occur. The internal organs of fish should be removed and disposed of. Fish should be rinsed well with clean drinking water before being cooked and eaten. 

Should pets or livestock drink water containing blue-green blooms? 

If livestock or other domestic animals have no other source of drinking water, they may be poisoned by drinking water from open water bodies, such as lakes or ponds, contaminated with blue-green algae toxins. Animals are not more sensitive than people to the effects of the toxins; they are simply not as concerned with the way water looks or smells before they drink it. 

Can water with blue-green algae blooms be used for recreational activities? 

Swimming and any other recreational activities (e.g., paddling) that may involve contact with the water should be avoided in areas where a bloom is observed. Blue-green algae toxins, if present, could be accidentally swallowed or inhaled. 

Why are public beach closures and risk advisories issued during blue-green algae blooms? 

Since some blue-green algae species can produce toxins that are harmful to humans, blue-green algae blooms are considered a public health concern and beach closures are issued. Closures also serve to remind users to check the water for the formation of highly visible blooms and scum (which pose the most risk) before entering. Since conditions may change in a matter of hours, being aware is crucial to making good decisions and staying safe. 

How long will a closure remain in effect? 

Beaches will remain closed until advisories for the applicable lake is lifted.  Advisories will remain in effect until no blooms can be visually observed and subsequent test results indicate that the water is within safe limits. Our website will be updated when beaches when are reopened. 

When is it safe to use the water again? 

If a risk advisory is in effect, it is not safe to use the water. If is no risk advisory is no longer in place and beaches are not closed for any other reason, then that particular lake has been deemed safe. It’s always a good idea to check the water before entering regardless of risk advisory or closure status as blooms can appear quickly and be suspended at different depths in the water where you can’t see them. So even if you can't see a bloom floating on the surface of the water, that doesn't mean one isn't present. After the toxin producing algae bloom is gone, toxins can remain in the water for several weeks. The time for water to recover to its normal state varies by bloom based on local conditions.  

How many lakes are monitored in the Halifax Regional Municipality? 

Staff regularly monitors 19 beaches across the municipality.  The municipality encourages lake users to use caution when visiting other lakes in the region. Users should check the water for surface scum, foam or a mat and/or discoloured water and be aware that blooms can be blue, blue-green, green, red, brown or yellow in colour. Some look like paint streaks on the water, while others many not affect the look of the water. If the water looks like this, it is best to avoid contact. 

What can be done to avoid algae blooms?

There are many factors that contribute to the growth of algae blooms—excess nutrients are among the most important of these. Limiting the amount of phosphorus and nitrogen that enters the watercourse helps to protect against bloom formation. This can be done by limiting the use of fertilizers, performing regular maintenance on septic systems and cleaning up after pets.