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The facts and fiction of blue-green algae in water bodies and how to distinguish it from ‘real’ algae

How we can prevent blue-green algae from showing up

June 1, 2022  By Julia Webber

Blue-green algae blooms along the shore of a lake. Photo credit: Smspsy/Shutterstock;

Each year as we near another summer, news articles of blue-green algae often rear their ugly heads. As we read these stories, they cause alarm that the algae in ponds, lakes and streams around us may not be safe. Let us look at blue-green algae together and explore what it is, why it can be of concern, how to figure out if you have it, and how to prevent it from showing up in your pond.

First things first, blue-green algae aren’t actually a type of algae, but rather a very misleading name. It can superficially look like algae, but it is not related and functions completely differently. In addition, it can be a dark blue-green colour, but it can also be olive green, brown or even red. To help with this, I am going to refer to blue-green algae as cyanobacteria for the rest of this article. This name is not only much more accurate but more importantly is a better descriptor.

What are cyanobacteria? Cyanobacteria, as the name would suggest, are a type of bacteria that use light to produce energy, just like plants and algae. This is part of the reason they are often green. They are generally single-celled organisms and can be invisible to the human eye unless there is a bloom. A cyanobacteria bloom is a rapid increase in number and quantity of organisms and is usually created when conditions are favourable.

Blooms can look like paint on the water surface that drifts with the wind and are most visible at shorelines but can also form below the water surface where they are not visible. They are most common in the late summer or early fall and thrive in shallow, slow-moving water but are not limited to them.


What is the big deal with cyanobacteria? The problem is that some types of cyanobacteria produce cyanotoxins which are very poisonous to humans, pets and wildlife. The most famous example of a cyanobacteria bloom is the red tide that is experienced in the ocean. The big problem is that there is no easy way to tell if the cyanobacterium in your pond is producing this toxin, so caution should always be used if you see or suspect it. As the density of cyanobacteria increases, such as during a bloom, so does this toxin. Cyanotoxins have a wide variety of symptoms, depending how you come into contact.

One of the common contact methods is ingestion while swimming. This can cause stomach pain, headache and neurological symptoms – for example muscle weakness and dizziness, vomiting, diarrhea and liver damage. Pets and livestock can also suffer severe symptoms by ingesting water by drinking water from a pond, stream or lake that has cyanobacteria in it. If you think there is cyanobacteria present, always prevent access to the pond.


A sign warns the public about the dangers of blue-green algae. Photo credit: Stephen Barnes/Shutterstock

Spotting the difference in algae
How can we tell if the “algae” in our pond is cyanobacteria or just normal algae? Unfortunately, there is no easy test that can tell you if there are cyanotoxins in your water. But there are a few DIY tests that can help us determine if cyanobacteria are present in your pond which were developed by the Kansas department of health and environment in 2012. I have included a link here for more detailed information on these tests (https://www.pca.state.mn.us/sites/default/files/wq-swm1-04.pdf).

Basically, there is a jar test and a stick test that will let you know if the most common cyanobacteria are present. As with all things these are not fool proof but certainly helpful and I would recommend reading the notes included in the document so you are aware of what they cover. More information is always better when evaluating for cyanobacteria.

What can we do to prevent cyanobacteria blooms? The most favourable conditions for most cyanobacteria are warm, still and nutrient-rich water. Although affecting the temperature of our water is not reasonable, it does help us to know when to be most alert for blooms. 

Water movement can be accomplished with an aeration system – either air diffuser aeration or a fountain – and has the added benefit of adding oxygen which greatly increases the health of any water body.

The most impactful way that we can prevent cyanobacteria blooms, though, is to reduce the nutrients that enter our water. Fertilizer, manure and compost are all nutrient rich and help our gardens and lawn look their best, but just as they make our lawns green so, too, do they make our water green. Preventing nutrients from entering our water can be done many different ways such as establishing berms around ponds so that water will filter through the ground before entering them; leaving a fertilizing buffer – an area that where no fertilizer is applied directly to it with the knowledge that when it rains it will absorb nutrients; applying nutrients only when there will be no excessive rain events; or applied in a form that is absorbed quickly into the soil.

Every property is unique, but managing the nutrients that could flow into our ponds and lakes will greatly help reduce not only cyanobacteria blooms but also algae blooms and excessive plant growth.

Although the cyanobacteria blooms are likely something we will continue to see going forward, there are ways that we can work together to help reduce them. As awareness grows on all levels and we work together to manage nutrient sources that may enter our waterways, we can help to reduce this not-so-pleasant part of our summer.

Julia Webber is president of Fish Farm Supply Co. Inc., which has been serving the lake and pond industry since 1989.

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