How to Shield Your Waters From Toxic Cyanobacteria Blooms

How to Shield Your Waters From Toxic Cyanobacteria Blooms

Emily Newton 27/11/2023
How to Shield Your Waters From Toxic Cyanobacteria Blooms

You might have encountered a cyanobacteria bloom if you’ve ever seen or smelled a pond covered with a thick, paint-green layer of slime.

Some cyanobacteria, which form clumps similar in appearance to algae, can actually be edible — but others can make you very sick if you ingest them. Learn what causes toxic cyanobacteria blooms and how to keep them out of lakes, streams and drinking water. 

What Causes Cyanobacteria Blooms?

Cyanobacteria are naturally present at low levels in many warm, slow-moving water sources. They also need sunlight for photosynthesis. What causes cyanobacteria blooms — the term for a sudden explosion in bacterial growth — is that the bacteria multiply faster than usual. 

Toxic cyanobacteria blooms can occur when artificial nutrient sources like cow manure, fertilizers or septic tank overflows find their way into the water. The combination of ample sunlight, warmth and nutrients allows the bacteria to proliferate. 

How can you protect your water against toxic cyanobacteria blooms?

Assess Your Water’s Vulnerability


The first step in preventing a cyanobacteria outbreak is to assess your water sources, because some are more vulnerable than others. Stagnant water is the most susceptible to cyanobacteria. 

You can also look at historical records of toxic cyanobacteria blooms in your water to see when or if they happened in the past. Did they occur during a particular season? The peak season for cyanobacteria blooms in many areas of the U.S. is from late May to early October, but it can vary due to local conditions and climate change. 

Climate change continues to worsen, as evidenced by frequent natural disasters, rising sea levels and higher temperatures. Cyanobacteria blooms will probably become more common as warmer temps and heavy precipitation extend their growing season.

Another way to predict cyanobacteria outbreaks is to evaluate how you use your land. Do you use fertilizers that could trickle down into your waterways? Do you raise animals whose manure could contribute to a bloom and further harm the environment? Studies have found that livestock-related activities produce 14.5% of emissions created by humans, worsening the climate crisis.

One way to assess your water’s vulnerability to cyanobacteria is by looking at upstream water sources. See if any waterways connected to yours are currently — or historically have been — contaminated with bacteria. 

Look for Signs of an Active Bloom


Your water system might not just be vulnerable to a cyanobacteria bloom — it might already be experiencing one. How can you determine if your water is contaminated?

Scum Formation

You might be able to see cyanobacteria growing in your water. Its colours range from blue-green to bright blue, green, olive green, grey or tan. The blooms can look like small clumps or fine grass clippings, and the water may appear murky.

Increased pH

You might notice your water’s pH has increased if you’re dealing with a cyanobacteria bloom. The bacteria remove carbon dioxide from the water as they photosynthesize, causing the pH to rise. 

A Strong Taste or Smell

A foul taste or odour is one sign of a cyanobacteria bloom in drinking water. It may taste or smell earthy, like rotting plants. In contrast, a fishy scent is usually associated with diatom blooms, which are not a type of cyanobacteria.

Take Action


If your water is contaminated, there are many steps you can take to clean it up. 


If your water repeatedly suffers from cyanobacteria blooms, one solution is to install a permanent form of treatment. Granular activated carbon (GAC), ozonation and membrane filters are cost-effective ways to filter cyanobacteria out of water. 

Ultrasonic Treatment

This new treatment technique oxidizes the water, destroying bacterial cells in the process. Ultrasonic waves interfere with cell division and photosynthesis in cyanobacteria. It’s useful for small-scale water treatment applications and causes no apparent environmental effects. Ultrasonic waves can potentially prevent blooms from forming if used preventively.

Before using this treatment, it’s a good idea to consult with your state or local government. It could increase the release of toxins in the water, so you may have to use another method to filter it afterwards. 


Aeration is another great tool for managing cyanobacteria blooms because stagnant water is one of the main causes. This technique involves pumping air through a diffuser on the bottom of a water source, releasing a plume of bubbles that rise to the surface. The air causes the water column to mix, disrupting the migration of the cyanobacteria’s cells and limiting their access to nutrients. It typically works well in small bodies of water. 

Mechanical Mixing

Another way to disrupt the nutrients in the water — making them harder for cyanobacteria to access — is by mechanically mixing the water. Mechanical mixers are usually mounted on the surface of a water body. They draw water from the bottom to the surface or move it from the surface level downward. 

These devices have a limited range. Water further away from them often remains stratified, meaning it isn’t mixed very evenly. Still, mechanical mixers are an environmentally friendly way to prevent cyanobacteria from growing uncontrollably. 


Algaecides kill true algae and cyanobacteria. There are so many different chemicals in this category that it’s hard to make a blanket statement about all of them. Some algaecides are environmentally safe, while others can harm fish and invertebrates living in the water. Some are safe for human consumption while others are harmful if swallowed. Do careful research before adding any chemicals to a water source, especially if you use it for drinking. 


When cyanobacteria form a thick scum on the water’s surface, you can skim a good portion of them off using a net. While this method won’t treat the entire body of water, it’s still a good way to reduce the overall quantity of bacteria growing in a pond or lake. 

Preventing Toxic Cyanobacteria Blooms

What causes cyanobacteria blooms? The main culprits are warm weather, stagnant water and sunlight, but fertilizer or manure contamination can also help the bacteria multiply. 

Keep a close eye on your water and look for signs of bacterial growth near the surface. Thankfully, there are many ways to prevent and treat an outbreak so you can enjoy clean, safe drinking water once more.

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Emily Newton

Science & Tech Expert

Emily Newton is the Editor-in-Chief of Revolutionized. She is a science and technology journalist with over three years covering industry trends and research. 

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