Blue-green algae

Blue-green algae, also known as cyanobacteria, live naturally in freshwater in Nova Scotia all the time. They are some of the oldest organisms on Earth.

There are many types of blue-green algae that appear in our water. Some are free-floating and form surface blooms when conditions are right. Others form into mats that grow on the bottom of a lake, river, pond or stream, and may wash up on shore once they die. 

Certain types of blue-green algae can occasionally produce toxins, known as cyanotoxins. The most common group of toxins produced by bloom-forming blue-green algae are microcystins, which mainly target the liver, kidney and digestive system.

Microcystins can have negative health impacts for humans if ingested, especially in high concentrations or consistently over a long period of time.

Mat-forming blue-green algae produce anatoxins, a group of toxins that target the nervous system and can be fatal to humans and other mammals (including dogs, if the mat material itself is ingested). 

We are still learning about the causes and consequences of mat-forming blue-green algae, but local research shows that even where mats of blue-green algae are highly toxic, the water above the mats is safe. 

Municipally supervised beach monitoring

The municipality monitors for blue-green algae at municipally supervised beaches from July 1 to August 31.

It is difficult to predict if blooms or mats will form. And it not possible to know if a bloom or mat will produce toxins by looking at it, even under a microscope. 

Blooms may vary considerably in colour, consistency and overall appearance. The presence of a bloom triggers the action of monitoring because toxins are only formed if there are blooms.

How is blue-green algae monitored at municipal beaches?

When a blue-green algae bloom or mat is detected in a lake with a municipally supervised beach, staff investigate at the beach. 

If suspected blue-green algae is observed, that beach will be closed immediately and a water sample will be taken to determine if toxin-producing species are in the water. 

If toxin-producing species are not present, the beach will reopen.

If toxin-producing species are present, the beach will remain closed until the bloom is gone. Staff will conduct water testing for toxins once the bloom or mat is no longer visible. The beach will re-open once samples of the water show that bacteria are within Health Canada guidelines.

Reporting suspected contamination

A bloom can appear as surface scum, foam, a mat and/or discoloured water. A bloom can be blue, blue-green, green, red, brown or yellow in colour. Some look like paint streaks on the water, while many others do not affect the look of the water. The municipality asks anyone who observes water conditions with these characteristics to call the provincial Inspection Compliance and Enforcement office at 1-877-9ENVIRO (1-877-936-8476) and Halifax Regional Municipality at 311.

Alerts and closures

Municipal staff monitor and report on the status of all municipally supervised beaches. Watch for advisories by visiting halifax.ca/beaches. Updates can also be found at www.NovaScotia.ca/Blue-Green-Algae.

The municipality monitors our supervised beaches for fecal bacteria, blue-green algae and other waterborne contaminants between July 1 – August 31 annually. If a suspected blue-green bloom is observed at one of our supervised beaches, the beach is closed immediately, and water samples are analyzed for toxins. The supervised beach is re-opened once water sample results are within Health Canada guidelines.

When a bloom is reported to the province in a lake where the municipality supervises a beach, municipal staff conduct follow-up monitoring for blue-green algae and perform water testing as necessary.

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 municipally supervised beaches.

Questions and Answers

What are blue-green algae (cyanobacteria)?

Blue-green algae, also known as cyanobacteria, are a group of microscopic bacteria naturally found in many types of water systems including ponds, lakes, rivers and wetlands. Blue-green algae are naturally present in fresh water in Nova Scotia. Under the right conditions (warm, slow moving, shallow water with enough sunlight and nutrients), blue-green algae can grow quickly. Some types of blue-green algae can float on the surface, while others grow along the bottom of a waterbody in what is called a benthic mat. In large quantities, some types of blue-green algae produce toxins that can be harmful to humans and animals.

What is a blue-green algae bloom?

Under the right conditions, floating blue-green algae can increase in numbers quickly, forming a bloom. A bloom can appear as surface scum, foam and/or discoloured water. A bloom can be blue, blue-green, green, red, brown or yellow in colour (see photos for both local and regional examples). Some look like paint streaks on the water, while others may not affect the look of the water. Blooms can smell like newly mown grass, or rotting garbage. 

When should I be watching for blue-green algae?

Blooms in the Halifax region usually happen between the early spring and the middle of fall. They may develop at other times of year, though, under the right conditions.

What causes a blue-green algae bloom?

Some conditions important for blue-green algae growth include: 

• Warmer water temperatures
• Enough light and length of daylight
• Wind and water currents (blooms often occur in slow moving shallow water, while mats tend to be found in flowing water)
• Excess nutrients (phosphorous/nitrogen)
• Suitable pH

What is the difference between an algae bloom and an algae mat?

Algae blooms and algal mats are two different types of cyanobacteria. Most cyanobacteria blooms float on surface of water or migrate within the water column. Other types grow as a thick mat on the bottom of shallow lakes or rivers. Benthic mats can be dark green or brown. When mats are newly forming, they are often covered in tiny bubbles. When they are dying back, they can look stringy and white, and can wash up onto shorelines. Toxins created by these mat-forming blue-green algae can be fatal to humans and other mammals, including dogs. As these mats decay, they may smell like rotting garbage. 

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

Do not swim or engage in any other recreational activity (e.g., paddling) that involves contact with water with a blue-green algae bloom. Keep children and pets away. 

If you find yourself in the middle of a bloom, do not panic. Exit the water immediately. Do not drink the lake water. Shower and towel off vigorously with clean water.

Monitor for symptoms, and if they develop, seek medical attention.

In areas where there are blue-green algae mats, keep your pet dogs on a leash until you have inspected the shoreline for mat material. Do not eat, or allow children or pets to eat anything they find on the shoreline. If you think that you, your child or your pet has consumed mat material, seek immediate medical attention.

You can report a suspected algae bloom by calling the provincial Inspection Compliance and Enforcement office at 1-877-9ENVIRO (1-877-936-8476) and Halifax Regional Municipality at 311.

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

If you swim in contaminated water, your eyes and skin may get itchy and irritated. You may also get hay fever-like allergy symptoms. Skin contact with blue-green algae toxins may cause result in hives, rashes, or blisters. You should wash with clean water as soon as possible after contact with a suspected algae bloom. If symptoms persist, seek medical advice.

What happens if you drink water contaminated with blue-green algae 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 could come on quickly and last for several days. Children and immuno-compromised individuals as well as pets 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, your eyes and skin may get itchy and irritated. You may also get hay fever-like allergy symptoms. Skin contact with blue-green algae toxins may cause hives, rashes or blisters. You should remove any affected clothing and wash the affected area with clean water as soon as possible. If you experience symptoms or health effects after recreational contact with affected water, seek medical advice.

How harmful are blue-green algae 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. See “What should I do if I come into contact with water contaminated with blue-green algal toxins?”

Exposure to low levels of toxins for long periods of time can potentially have long-term or reoccurring effects in humans.

Children are at greater risk than adults of developing serious liver damage from ingesting algal toxins, mostly because of their comparatively lower body weight and increased likelihood of consuming water while swimming. Immuno-compromised individuals as well as pets are also at a higher risk for the more severe effects.

The toxins commonly found in benthic blue-green algae mats can be fatal if the mats are ingested. They have been known to cause fatalities in dogs in Nova Scotia, 

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

No, you should not drink water if the source waterbody has blue-green algae blooms. Since toxic blooms cannot be identified by sight and need to be tested, exercise caution and assume that toxins are present. If you receive your drinking water directly from a source that has a confirmed 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 drinking water. Also note, boiling water does not remove blue-green algae toxins from drinking water.

If you are connected to a municipal or registered water supply, you can continue to use water as usual, unless notified by the system owner/operator. While algal blooms do not happen naturally in groundwater, contaminated water from lakes, ponds or streams can enter nearby shallow dug wells and improperly sealed drilled wells.  If your well is near a body of water that has a confirmed bloom, you should exercise caution and use an alternative water source wherever possible.

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 algae toxins for washing? 

If a safe source of water is available, don't use contaminated water for washing clothes or dishes, as you will risk the negative effects of skin contact with algal toxins. If no alternate safe source of water is available, then you may use contaminated water for washing laundry or dishes. Exercise caution while doing so, by using rubber gloves to avoid direct contact with the water. Rinse dishes with water from a clean, alternate source.

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 algae toxins? 

Toxins can accumulate in the tissues of fish, particularly in the internal organs (liver, kidney, etc.). Toxin levels in 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? 

No. Livestock and domestic animals may be poisoned by drinking water contaminated with blue-green algae toxins. Animals are not more sensitive to the effects of the toxins; they are simply not as concerned with the way water looks or smells before they drink it.

Do a visual inspection of the water before letting your pets or livestock enter or drink the water. If you suspect the animal has ingested water containing a blue-green algae bloom, contact a veterinarian.

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. Skin contact with blue-green algae toxins may result in a rash, blisters or itchiness.  OR See “What happens if you swim in water contaminated with blue-green algal toxins?” for symptoms of skin contact with blue-green algae.

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 mats (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 toxin levels in the water are within safe limits. Our website will be updated when beaches 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. Even after a risk advisory has been lifted it is recommended that you visually check the water before entering, as blooms can appear quickly. Even if you can't see a bloom floating on the surface of the water, or along the bottom of the lake or river, 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 along the bottom of the waterbody 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 may not change the look of the water. If you see any growths in the water that fit these descriptions, it is best to avoid contact. 

What can be done to avoid algae blooms?

Though it is difficult to predict whether a bloom will form, most type of blue-green algae blooms require nutrient-rich waters to grow quickly. 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, setting up naturalized buffer zones around water bodies, performing regular maintenance on septic systems and cleaning up after pets. Visit the municipality's Canine for Clean Water Campaign to learn more about the importance of picking up after your dog.