A Closer Look at Algae

Algae is a summer constant, and a constant source of worry for many cottagers. The presence of algae in the Georgian Bay area is often seen as a sign that something is wrong. Whether it be a faulty septic system, or phosphorus pollution, people worry that the algae they are seeing are the result of human interference.

Algae can cause problems during the summer. An excess of algae – called an algal bloom – tend to reduce water quality for recreational activities, can lend odd tastes and colour to drinking water, and in some rare cases can be harmful to humans and animals. Additionally, the algae that people have been seeing in recent years is changing, both in type and location. We don’t know exactly why that is, given that the nutrient cycles of Georgian Bay that influence algae growth are complex, but we do know that despite common negative views on algae, it’s a natural part of the aquatic ecosystem.

Algae is not only natural, but also vitally important to the Georgian Bay aquatic food web. Both in smaller amounts and as blooms, algae act as food and producers of oxygen, both of which are extremely important to the health of our Bay. While some algal blooms can be dangerous, it is important to be able to recognize when you are seeing harmful versus harmless blooms. To work on our aquatic health, we need to know a few things: what is algae, when is it dangerous, and what do we do about it?

What is Algae?

What we call ‘algae’ are actually a diverse group of organisms, not all of which are necessarily plants. They are all joined by the fact that they are simple, aquatic organisms that photosynthesize. This means that they create their own energy from the sunlight, taking in carbon dioxide and producing oxygen. This is one of the reasons that algae is incredibly important; half the oxygen we breathe is produced by algae.

Algae is also widespread, able to exist anywhere that there is moisture. Algae can be found in all of our lakes and rivers, and is known as a ‘primary producer’. Primary producers create their own food, and are the base of most aquatic food chains. As algae is at the base of our aquatic food chain, its presence is vital to the health of every creature that lives in and around Georgian Bay.

In the Georgian Bay area, there are three general types of algae that you might see during the summer months: filamentous green algae, chrysophytes, and blue-green algae.

Filamentous Green Algae

Filamentous green algae looks like what most people picture when they think of algae: collections of green algae that tends to form in strands. These strands are made up of multiple single-or-multicellular organisms, and are either free-floating in pillowy clumps, or attach themselves to submerged rocks, logs, or other objects.


Chrysophytes are unicellular microorganisms, which can grow in colonies that make the water cloudy and tinged yellowish-green. Chrysophytes bloom most often in spring and early summer, and they tend to thrive in low-nutrient lakes.

Blue-Green Algae

Blue-green algae is actually a photosynthesizing bacteria, and blooms most often occur in the late summer and into the early fall. These blooms look bluish-green, and can be dangerous to humans and animals.

Algal Blooms

It is important to note that, even though these types of algae are always present in our lakes and rivers, this doesn’t mean we can always see them. Most of the time, algae exist in our water in microscopic forms not visible to the human eye. Algae is only visible when blooms occur, which require specific conditions.

For a bloom to occur, algae require still water, warm temperatures, and sufficient nutrients. If these conditions are met, the existing algae in the water will multiply rapidly to the point where they are visible to the naked eye. These growths are blooms. While some algae growth is natural and beneficial to aquatic ecosystems, excessive blooms can be detrimental for a few reasons.

When algae bloom, there are millions of individual organisms reproducing, and then dying off. When the algae die they sink to the bottom of the lake, and are consumed by bacteria. These bacteria use up the oxygen in the water under the bloom, resulting in an under-oxygenated area – a ‘dead zone’ where other creatures can’t survive. Additionally, excessive algal blooms can affect water quality, making lake water cloudy and foul smelling.

While most algal blooms can cause a reduction in water quality and lead to problems for aquatic animals in excess, most are not harmful to humans. However, Harmful Algal Blooms (HABs) do exist, and in the Georgian Bay area, they come from blue-green algae blooms. Here are a few key ways to tell if an algae bloom you see is blue-green:

Blue-Green Algae Bloom Identification
  • A blueish-green tint to the bloom, which may look like turquoise paint or green pea soup
  • Denser blooms form clumps
  • Fresh blooms smell like freshly-mowed grass, while older blooms smell like rotten garbage

If you detect a likely green-blue algae bloom, you should:

  1. Stop drinking, using, and swimming in the water
  2. Don’t let pets near the water
  3. Contact the Ontario Ministry of the Environment, Conservation and Parks’ Spills Action Center, at 1-800-268-6060

Preventing Algal Blooms

While some algae is perfectly natural and beneficial to the environment, an excess of nutrients such as phosphorus in the water can lead to extensive blooms. Here are a few ways to prevent the introduction of algae-growing nutrients into the water on your own property:

  • Any soaps, detergents, or fertilizers that you use should be phosphate-free, and not allowed to drain directly into the lake
  • Adding a buffer-zone of native plants along your shoreline, so as to reduce runoff from your lawn going directly into the water
  • Make sure that your septic system isn’t leaking (a healthy septic system will keep in waste, but if it is leaking you will notice smells and seepage)

While we know that the types and occurrences of algal blooms in the Bay and our inland lakes are changing, we don’t know exactly what’s happening. Understanding environmental changes takes time, and monitoring. Water quality monitoring is an effective way to determine what phosphorus concentrations are ‘natural’ for your lake, and track trends to learn if things are getting better, worse, or staying the same. To learn more about water quality monitoring, visit the Lake Partner Program website.

Sarah Vokey is a Science Communication Summer Intern at the GBBR. A native of Sudbury, Ontario, Sarah has a fierce love for the natural beauty of Georgian Bay, and is thrilled to be working with the GBBR. You can reach Sarah at [email protected]

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