Many of you have recently reported the presence of unknown vegetation growing along the shoreline. It is easy to confuse filamentous algae, aquatic plants and cyanobacteria. The proliferation of these types of “vegetation” is certainly the sign of a productive watercourse that is chock full of nutrients. All this vegetation is a good indication of the ecological state of a watercourse.
Filamentous algae appears in many ways: it is hairy and accumulates in mats or scummy mass, sometimes resembling moss and can cause small cushions or rugs, none of which are inviting to swimmers. Some even resemble gelatinous nets that can be lifted with a stick or by hand. They are not noxious to your health and can simply be removed from the water.
Hot weather and stagnant water enhance their development. They are particularly abundant at the beginning of the summer season because they are the first to feed on the nutrients in the water. These algae generally represent a short biological cycle influenced by the quality of the water and the aquatic habitat. Certain species of filamentous algae can even exist during the winter months in a vegetative state, like cyanobacteria.
Filamentous algae can be found attached to many types of surfaces: rocks, branches, sand beds, etc., in depths ranging from a few cm to a full metre. They can also develop in a stagnant water pool and float freely. Because of the effects of currents and winds, they can move to certain areas such as the backs of bays.
When it comes to aquatic plants, RBL has published a brochure that illustrates several examples of immersed, emerging or floating plants. Aquatic plants possess roots, stems and leaves. They grow throughout the season. Boat propellers chop them up and help them spread and replant. Direct sun and warm water have great influence on waves of algae and the development cycles of different species. Please also note that filamentous algae and aquatic plants are frequently found joined together in the same vegetation mass as the adjoining photo indicates.
To conclude, let’s talk about cyanobacteria. These organisms are closer to bacteria than algae. They are semi-bacteria and microscopic (not visible to the naked eye); they are semi-algae because they are capable of photosynthesizing like filamentous algae and aquatic plants. Cyanobacteria live in the water table. Many species are capable of moving vertically to get maximum benefit from available nutrients and light. On the water surface they can form green trails of vegetation. A bloom is made up of millions of cyanobacteria accumulated in the water table, giving it a green colour.
This green colour is due to the chlorophyll content found in the cyanobacteria cells. A deposit of scum along the shoreline or on the water surface is an indication of a large concentration of accumulated cyanobacteria from the effects of the wind and waves. To the eye, it is either a brocoli soup or green paint that generally appears toward the end of the summer season even though they can be found in any locality at any time. Any contact with the scum should be avoided because the cyanobacteria can cause irritation to the skin, mucous membranes and bring on gastro-enteritis. As well, some species may contain toxins that are considered a health nuisance