Blue-green Algae1

Algues bleu vert- General
- Causes
- Recognize It, Report It, Prevent It



Blue-green algae, or "cyanobacteria" by their scientific name, are microorganisms that have existed for over three billion years. They are naturally present in the lakes and rivers of Québec at low concentrations. Normally they do not cause any problems. However, under certain conditions blue-green algae can reproduce quickly and become extremely abundant. They then form what are called "algal blooms". These blooms look like paint spills, broccoli soup, or a mixture of fine particles or very short fibers. They are usually green or blue-green but may occasionally have a reddish tint. Near shorelines, blooms rise and form a surface scum that may emit an unpleasant odor. In addition to looking repulsive, blue-green algae blooms produce toxins that can be harmful to human and animal health. Whether a body of water experiencing such blooms can be used for recreational or other purposes depends on the level of toxins that the algal blooms produce.


The proliferation of blue-green algae can be triggered by a variety of factors such as elevated water temperature, weak current or water stagnation. However, the major factor in their proliferation is the level of phosphorus in the water.

Phosphorus is an element that is essential to life. It is a basic nutrient for many forms of life including plants, animals, algae, and .... bacteria. We use phosphorus to fertilize our lawns and gardens and to help stimulate crop growth.

Phosphorus naturally occurs in surface waters but at low levels. Unfortunately, many human activities can lead to higher phosphorous levels in aquatic environments. Excessive phosphorus is found in domestic wastewater and in drainage/runoff from deforested and/or cultivated fields and from shorelines that have been enriched with chemical fertilizers, compost, and/or solid or liquid manure. Eventually this phosphorus finds its way into our lakes, rivers, and streams. When present in sufficient quantities, it stimulates growth of certain organisms found in these waterways. Some of these organisms make excellent use of this excess phosphorus which is the case with many aquatic plants (eg: Eurasian milfoil) and with blue-green algae.

Recognize It, Report It, Prevent ItAlgues01 P1010042

Recognize It

Blue-green algae blooms can be difficult to distinguish from other aquatic phenomena. Fortunately, the Ministère du Développement durable, de l'Énvironnement, et de Parcs (MDDEP) has produced a very helpful guide to identifying them. This guide is available from your regional MDDEP office2 and on line at (2,96 MB - French only)

Report It

If you think you have witnessed a blue-green algae bloom, report it! Even if the bloom quickly disappears, report it anyway - blue-green algae blooms move around beneath the surface of the water and can reappear later the same day or the next day. To report the bloom, contact the regional MDDEP office in Gatineau2 at 819-772-3434 (Fax 819-772-3952; Email: This email address is being protected from spambots. You need JavaScript enabled to view it.). Better yet, complete the reporting form provided at (French only) and submit it plus photos of the bloom to the Ministry. Don't forget to notify your municipal office of the sighting and advise the Blue Sea Lake Watershed Association This email address is being protected from spambots. You need JavaScript enabled to view it.. Also, don't hesitate to contact one of the Association's directors if you need help translating and/or completing the reporting form.

Please note that the Ministry might ask you to take a sample from the blue-green algae bloom. Click here for the directions on how to do so. If you have any questions regarding this protocol or need assistance in taking a sample, please contact one of the Association's directors.

As there can be public health issues associated with blue-green algae blooms, it is imperative that you report them.

The MDDEP will confirm the presence of algae blooms in affected lakes and rivers by taking samples and analyzing them. It also informs public health authorities who will issue health advisories as necessary detailing specific recommendations re water consumption for the affected waterway. For more information regarding the possible health effects of blue-green algae, visit the Ministère de la Santé et des Services sociaux (MSSS) website at

Prevent It

The best way to deal with blue-green algae proliferation is to prevent it by attacking the source of the problem (ie: an overabundance of phosphorus in our lakes and rivers). There are a wide variety of ways to help reduce the inflow of phosphorus into our water system. These include:

  • retaining or, if applicable, restoring shoreline vegetation; such vegetation uses phosphorus as a nutrient;
  • eliminating the use of chemical fertilizers, compost, or manure on lawns;
  • using only phosphate-free soaps, detergents, and other cleaning products;
  • ensuring the proper functioning and regulatory compliance of septic systems.

Preventing an overload of phosphorus in surface water and upstream watersheds remains the best way of countering blue-green algae blooms. Such preventative action requires the combined efforts of all citizens, businesses, and government authorities.

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The text is based on the article "Blue-green algae and our surface water" found in the MDDEP website - modified slightly for our association use.

2 Regional Office of the MDDEP – Outaouais
98, Lois St
Gatineau (Quebec) J8Y 3R7
Telephone : 819 772-3434
Fax : 819 772-3952
This email address is being protected from spambots. You need JavaScript enabled to view it.