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Cyanobacterial blooms

Cyanobacterial Blooms – Causes and Treatment

Cyanobacteria, also known as blue-green algae are found in the oldest known fossils, dating back 3.5 billion years. They were the organisms that caused the first mass extinction on earth, but are also the reason for the earth as we know it today. They released the first oxygen molecules into the atmosphere. Today, cyanobacteria are still common in waterbodies all over the world. Cyanobacterial blooms can lead to a depletion of oxygen in the water, a release of toxins, as well as taste and odour problems.

Jump to section:
1. Definition
2. Bloom causes
3. Impact of cyanobacterial blooms
4. Treatment methods

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Remote sensing images from the Dutch water treatment company LG Sonic, obtained from satellite data, show in detail the algae levels in lake Okeechobee:

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Cyanobacteria definition

Cyanobacteria (blue-green algae) are microscopic bacteria found in freshwater lakes, streams, oceans, damp soil, moistened rocks and even sloth fur. Even though they are bacteria, cyanobacteria are too small to be seen by the naked eye, they can grow in colonies which are large enough to see. When algae grows too much it can form “blooms”, which can cause various problems. Cyanobacterial Harmful Algal Blooms (CyanoHABs) are dangerous to people, animals, or the environment and can lead to a depletion of oxygen in the water and a release of toxins, as well as taste and odour problems.

Most cyanobacterial blooms are clearly visible. They form a layer on top of the water, which can be various colours including green, blue, brown or red. It sometimes seems as if there is a layer of paint on top of the water. They are capable of moving through the layers of water. During the day they travel to the surface to collect sunlight for energy, enabling them to photosynthesize. At night they travel to the bottom of the water for nutrients. This process enables the cyanobacteria to grow.


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There are various types of cyanobacteria, both toxic and nontoxic. One specific type called “spirulina” is considered to be a very healthy food source, and was consumed regularly by the Aztecs. Nowadays spirulina is sold in health stores in powder or tablet form. Conversely, cyanobacteria can produce toxins (such as microcystins and anatoxins) that affect people, livestock and pets after swimming in and drinking from algae-contaminated water.

Cyanobacterial bloom causes

Algae are needed in many waterbodies as they provide oxygen, and are a food source for other marine species. In moderation, the algae provide balance for a healthy water ecosystem. However, due to reasons such as climate change, cyanobacteria can grow to excess, causing cyanobacterial blooms, which occur when there is enough sun, the water is warm, stagnant or slow moving and if there are enough nutrients such as phosphorus and nitrogen present in the waterbody. The blooms are more common during late summer or early fall. Current nutrient pollution is also exacerbating the problem, increasing the number of cyanobacterial blooms that occur.

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Climate change and harmful algal blooms

Climate change occurs naturally as well as being caused by anthropogenic activities over the decades. In both fresh and marine water, a concentration of greenhouse gases results in  a rise in the water surface’s temperature, a lower pH, changes to precipitation, evaporation and vertical mixing of water. All of these consequences of changing the environment, in combination with excessive levels of nutrients are potentially contributing to CyanoHABs in many waterbodies.

Nowadays the visible signs of global climate change are evidenced in the numerous massive algal bloom events we are observing worldwide, driven by warm water conditions. Hence, NASA has joined the effort to identify and record the algal bloom events. Satellite images show that the extent of algal bloom in the oceans and lakes has been exceeding expectations, as an example, in August 2015 the Baltic Sea toxic blooms of cyanobacteria were accelerated by warm sea temperatures.

Satellite image of an algal bloom

Satellite image of an algal bloom.

Nutrient pollution

Nutrient pollution is the process in which too many nutrients, mainly nitrogen and phosphorus, enter waterbodies, causing excessive algae growth. Changing precipitation patterns, melting glaciers and intensifying storms have resulted in the escalation of nutrients. They also promote eutrophication, which is a process induced by increased nutrients, especially nitrogen and phosphorus, in waterbodies resulting in algae and plant growth. This phenomenon can take place naturally, but the anthropogenic input of nutrients, also called cultural eutrophication, is considered a major factor. Fertilisation of arable land, sewage discharging, industrial effluents, use of detergents and extensive livestock farming are some of the activities that are responsible for the anthropogenic input of nutrients.

The increased availability of nutrients is causing changes in lakes from oligotrophic, which are cold, low in nutrients and clear, through mesotrophic to eutrophic, nutrient-enriched lakes. Some examples are Lake Mälleran – Sweden; Lake Biwa – Japan, Lake Constance between Germany, Switzerland and Austria, Lake Balaton – Hungary, Lake Taihu – China, the Great Lakes in North America and many others.

Impact of cyanobacterial blooms

When cyanobacterial blooms occur, they damage the water ecosystem, causing fish and plants to die off due to the overpowering algae. The water quality decreases as it turns green, and it can also produce a bad odour as the algae in the bloom start to die off.

Besides the environmental impact, it might also have an economic impact, because recreational water areas might have to be closed due to toxic cyanobacterial blooms. Also, costly treatments might have to be introduced. If a bloom occurs in, for example, a drinking water reservoir, the company may not be able to provide enough drinking water. Thus, it is at risk of running at a financial loss if action is not taken in time.


Some cyanobacteria release a toxin called cyanotoxin, which is produced and contained within the cell, and is mostly released after cell death or if cells are lysed open. However, some species of cyanobacteria can release toxins without the occurrence of cell death or lysing. Cell deaths occur naturally but also after actions have been taken to treat the CyanoHABs. Cell lysing occurs during certain types of treatments. A sudden release of these toxins can be harmful to humans, animals and the environment.

Drinking water supplies have also been at risk in the past few years, not only facing taste and odour problems but also resulting in public health issues. Toledo, Ohio shut down the water supply service to 500,000 people last year during an algal bloom; thirty-five million dollars has been spent in 2015 to fight algal blooms in Chaohu Lake, the fifth largest freshwater lake in China, which is struggling to supply local residents with potable water; Indian Lake (USA) was closed for the summer in 2015 due to blue-green algae.

If humans come in contact with cyanotoxins, either by drinking contaminated water, inhaling it or eating contaminated fish, it could affect the liver (hepatotoxins), the nervous system (neurotoxins), the skin and even increase tumour growth (dermatoxins). There are also many reported cases of domestic and wild animal illness and death linked to cyanotoxins.

Cyanobacteria treatment methods

There are various methods to treat CyanoHABs including physical removal, chemical procedures and biological inactivation. However, understanding of the specific toxin is vital for treating the CyanoHABs because each toxin is treated individually in varying intensity.

The most commonly used method is chemicals, including copper sulphate and hydrogen peroxide, despite the fact that these methods are harmful to the environment. When these substances are used, they cause sudden death or lysing of cyanobacteria cells, thus a sudden release of large amounts of cyanotoxins occur. Another factor to consider is that these methods do not take care of the core problem, as blooms can occur again after the treatment.

There are also natural ways of treating cyanotoxins. One example is reducing the amount of nutrients that get into the water. Nutrients enter the water in various ways, two examples are via animal waste and fertilizers. There are various ways of preventing entry, however it may be difficult to attain and will take a long time to be effective.

In order to prevent the use of chemicals but still have an effective treatment, LG Sonic has developed an ultrasound technology to control algal blooms. The ultrasonic system controls the algal blooms by creating a sound barrier on the top layers of the water, so that the cyanobacteria can no longer reach the water surface and therefore can no longer grow. However, because they are still a vital part of the water ecosystem, the ultrasonic algae control does not eliminate the cyanobacteria completely but reduces them by up to 90 %. This restores the water ecosystem by reducing and controlling the algae levels.

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  • LG Sonic B.V.
  • Heliumstraat 7
  • 2718 SL Zoetermeer
  • The Netherlands