The blue-green algae found in our watercourses are microscopic organisms that go by the scientific name of cyanobacteria. They are similar to bacteria, but share some of the features of algae. Where conditions are favourable, they are able to multiply and form blooms. The blooms produce toxins that can be harmful to human and animal health.

Proliferation of Blue-Green Algae

Under some conditions, blue-green algae proliferate rapidly and form what is called a bloom. The name may seem somewhat poetic, but the phenomenon is actually quite unfortunate and bears no resemblance whatever to a flower! Algae blooms in fact look more like a paint spill, or broccoli soup: a minute particle or very short strand slurry. Visible to the naked eye, they are often green or blue-green in colour, sometimes edging towards red. Near shorelines, blooms rise and amalgamate into surface scum and may emit an unpleasant odour. In addition to looking repulsive, algae blooms have the ability to produce toxins. The use that can be made of a body of water depends on the level of its contamination by these toxins.

The Causes

Blue-green algae proliferation can be triggered by a variety of factors such as elevated water temperature, weak current or water stagnation. However, the main guilty party is phosphorus.

Phosphorus is an element that is essential to life. It forms part of the basic building blocks of our nutrition, just as it does for animals, plants, algae and even bacteria. We use phosphorous to fertilize our lawns and gardens and it is employed in agriculture to stimulate crop growth.

Phosphorous has a naturally occurring low presence in surface waters. However, many human activities can lead to higher phosphorous levels in aquatic environments. Excess phosphorous is found in domestic wastewater and drainage, leaching from septic systems, and runoff from deforested land or cultivated fields and shorelines that have been enriched with fertilizers, compost and solid or liquid manure. Eventually, the phosphorous finds its way into rivers and lakes. When present in excessive amounts it stimulates inordinate growth of certain organisms that are native to these bodies of water, which includes many aquatic plants, and unfortunately, especially blue-green algae.

What can you do to reduce this risk?

Recognize it, report it, prevent it!

Learn to recognize it

Algae blooms may be difficult to distinguish from other aquatic phenomena. This is why the Ministère du Développement durable, Environnement et Lutte contre les changements climatiques du Québec (MDDELCC) has produced a helpful guide to identifying and preventing them. The guide is available from your regional MDDELCC office or at this link.

If you spot it

Take a cautious approach, as some varieties of this algae can produce toxins that are harmful to both humans and animals.

If you suspect a blue-green algae bloom:

– Assume toxins are present

– Avoid using, drinking, bathing or swimming in the water (call your local health unit for swimming advisories)

– Restrict pet and livestock access to the water.

– Contact your local health unit for information on health risks associated with blue-green algae blooms.

Report blue-green algae blooms

If you spot blue-green algae blooms, contact the Outaouais office of the MDDELCC.

Has the bloom you noticed this morning already disappeared? Report it anyway, since blooms move around beneath the surface of the water and can reappear later on in the day or the next day.

If you wish to make your action even more efficient you can photograph the bloom and complete this form and send it by fax or email to the MDDELCC. You can also call the Ministry and ask to speak to the person responsable for cyanobacteria.

170 l’Hôtel-de-Ville St., office 7.340
Gatineau, QC J8X 4C2
Telephone: 819 772-3434
Fax: 819 772-3952

For more information regarding the Quebec government’s Intervention Plan on Blue-Green Algae, you can visit this link.


It is not easy to overcome the phenomenon of blue-green algae proliferation, but the best way is to attack the source of the problem. Above all, we need to avoid an overabundance of phosphorus in our lakes and rivers and there exist simple and easily accessible ways achieve this goal.

Take these simple steps to prevent the growth of blue-green algae:

– Use phosphate-free detergents, personal care and household cleaning products

– Avoid using fertilizers, compost or manure on lawns, especially fertilizers that contain phosphorus

– Maintain a natural shoreline on lake and riverfront properties; restore shoreline vegetation or avoid clearing it away, because shoreline vegetation retains soil that is potentially rich in phosphorus and uses this fertilizing element for growth.

– Reduce agricultural runoff by planting or maintaining vegetation along waterways and minimizing fertilizer use

– Check septic systems to ensure they do not leak into the water source.

Preventing phosphorus overload in surface water and upstream watersheds remains the best way of countering blue-green algae proliferation. This preventive action requires collective efforts on the part of citizens, enterpises and municipal and provincial government authorities.

Who does what?
The MDDELCC confirms the presence of algae blooms in affected lakes and rivers, takes samples and analyzes them. It also informs public health authorities, which then issue health advisories as necessary. These advisories allow for timely communication of specific recommendations for the affected bodies of water with respect to limits on water consumption.

The Ministère de la Santé et des Services sociaux (MSSS), for its part, makes general recommendations on drinking water, swimming and other aquatic and nautical activities available on its website at this link.