Cyanobacterial blooms

In short

  • Cyanobacterial blooms have become a global challenge due to rising temperatures caused by climate change;
  • The spread of harmful algal blooms is a growing concern for societies worldwide;
  • There are various methods to tackle algae growth, including physical removal, chemical procedures, biological inactivation, and ultrasonic control.

Cyanobacteria (blue-green algae) are one of the most common organisms on Earth. They appeared over 3.5 billion years ago, reshaping our entire biosphere. It’s believed that cyanobacteria photosynthesis enriched Earth’s early atmosphere with oxygen, giving rise to life as we know it.

Throughout history, cyanobacteria have evolved to adapt to various geochemical and climatic changes. Modern cyanobacteria have learned to exploit human modifications of the aquatic environments. Nutrient over-enrichment and hydrologic alterations have dramatically affected global water ecosystems. Accelerated by climate change and its consequences, cyanobacterial blooms have become a global concern.

What is cyanobacteria?

Cyanobacteria definition: microorganisms that structurally resemble bacteria, but lack a nucleus and organelles. Unlike other bacteria, cyanobacteria can conduct oxygenic photosynthesis and contain chlorophyll a (chl-a).

Cyanobacteria have a remarkable capacity to somehow adapt to global changes. They can survive high ultraviolet light, desiccation, hypersalinity, and extreme temperatures even for many years.

These organisms grow in freshwater lakes, streams, oceans, damp soil, moistened rocks, and more. Over billions of years of evolution, they have formed unique symbiotic associations with microorganisms, plants, seagrass, fungi, sponges, and cycads. They even live on sloths’ fur and polar bears.

Single cyanobacteria are too small to see without a microscope, but they can grow into massive colonies, which can even be seen even from space. Cyanobacterial blooms can be extremely dangerous to human health, animals, and ecosystems.

Dangers of harmful cyanobacterial blooms

The spread of cyanobacterial blooms (cyanoHABs) has become a significant concern for societies worldwide. Cyanobacteria can critically impair the safety of drinking water, and fishing, irrigation, and recreational value. CyanoHABs deplete the oxygen in the water, release toxins, and degrade the water quality.

Environmental impacts

Cyanobacterial blooms can severely damage water ecosystems, causing fish and plants to suffocate and die. They compromise the water quality and safety for animals and people by releasing cyanotoxins into the water. When the cyanobacteria in the bloom start to disintegrate, they produce unpleasant tastes and odors.

Economic impacts

CyanoHABs can bring economic losses to many business sectors. They cause significant financial damage to the agricultural sector, fisheries, water treatment plants, tourism industries, recreational services, and real estate prices in the waterfront areas.

Health impacts of cyanobacterial blooms

Some cyanobacteria can release toxins (cyanotoxins), which are produced and contained within their cell. Cyanotoxins are released after the cell death or if the cells are lysed open by chemical treatment. These toxins can be dangerous to humans, animals, aquatic life, and the environment.

If people consume cyanotoxins by drinking contaminated water, inhaling them while swimming, or eating contaminated fish, they can affect their liver (hepatotoxins), their nervous system (neurotoxins), and skin. They can cause kidney damage, abdominal pain, shortness of breath, and can increase tumor growth (dermatoxins). Reported cases of domestic and wild animal illnesses and death linked to cyanotoxins are growing each year.

Both long-term exposure to low toxin levels, and short-term contact with high toxin levels deteriorate health. For water managers, it is crucial to know if drinking water contains blue-green algae and associated toxins. Therefore, it is essential to comply with current drinking water guidelines for toxins to minimize public health risks.

Cyanotoxin production depends on environmental factors. Nutrient supply rates (nitrogen – N, phosphorus – P, and trace metals), light intensity, and high temperatures have a major impact. Interactions with other bacteria, viruses, and fish can also stimulate the release of cyanotoxins into water bodies.

What causes cyanobacterial blooms?

Anthropogenic nutrient enrichment, altered hydrologic patterns, and changes in the Earth’s climate accelerate the intensity, duration, and frequency of cyanoHABs. Extensive nutrient supply (N and P), rising atmospheric CO2 levels, and higher water temperatures intensify the cyanobacterial growth. Vertical stratification, water residence time, and interactions with other biota are also contributing factors.

Nutrient pollution feeds cyanobacteria

Cyanobacteria are actively exploiting human-made pollution of water systems. They thrive on nutrient pollution and eutrophication. Urban, agricultural, and industrial activities increase nutrient pollution, salinization, and eutrophication of waterways. This stimulates more frequent and persistent HABs.

Climate change exacerbates Cyanobacterial blooms

Climate change is another powerful catalyst for Cyanobacterial expansion. Rising temperatures and changes in the precipitation patterns stimulate more frequent and extensive cyanoHABs. Elevated temperatures lead to an earlier onset and longer duration of thermal stratification, making the buoyant cyanobacteria more competitive.

The response of cyanobacteria to the increase in temperatures strongly depends on nutrient availability. Climate changes alter the precipitation and biogeochemical processes that make nutrients more available for cyanobacteria to thrive.

Cyanobacterial blooms accelerate climate change

CyanoHABs draw down the CO2 from the atmosphere, turning lakes into CO2 sinks.
A study published in Science Advances concludes that cyanoHABs produce significant amounts of greenhouse gas methane during photosynthesis. Substantial methane production rates are observed under diverse conditions – light, dark, oxic, and anoxic.

This creates a positive feedback loop: higher global water temperatures stimulate more cyanoHABs, which emit more methane, contributing to global warming.

What causes moldy smells and taste?

Unpleasant taste and odor are mainly caused by two metabolites produced by a range of cyanobacteria and actinomycete bacteria: 2-methylisoborneol (MIB) and geosmin. These are important indicators of drinking water quality and may be subject to customer complaints. They are evident at very low levels (from 500 cells mL-1); therefore, early water treatment is advised. Unpleasant taste and smells become and issue during warmer months when higher temperatures encourage algal growth.

Despite its earthy and musty taste and odor, the water may not be unsafe to drink. Contrary to common belief, the absence of compounds does not guarantee that water is safe for consumption. There are guidelines in place to bring clarity. The Australian Drinking Water Guidelines, for instance, distinguish two types of guideline value: a health-related guideline value, and an aesthetic guideline value.

Drinking water guidelines

Drinking water quality guidelines advise tolerable levels for components that can threaten public health; therefore, they are essential for water supply authorities. Respective states, regions, or countries develop guideline values based on The World Health Organization (WHO) Guidelines for Drinking Water Quality. These guidelines exhibit a scientific agreement on the health hazards presented by chemicals and microbes within drinking water supplies.

The guidelines are fundamental for developing adequate risk management strategies. Examples of guideline values for the concentration of total microcystins in drinking water that must be met in individual countries are as follows:

  • Australia: 1.3 μg L-1;
  • South America: 1.0 μg L-1;
  • Canada: 1.5 μg L-1;
  • WHO: 1.0 μg L-1;
  • USA: Cyanotoxins are currently accepted as unregulated contaminants and may require regulation under the Safe Drinking Water Act.

What should water managers monitor?

First, it is crucial to know which algae species are present in the water body, as well as the level of dissolved toxins, cell counts, and taste and odor compounds. The latter cannot be directly linked to cyanobacterial toxicity; it can only be used for assessment and not as a base for a warning system. The assessment facilitates a better understanding of the cyanobacterial problem. Depending on the initial results, management can implement The Alert Levels Framework, drinking water guidelines, control measures, or water treatment.

Microscopic examination and enumeration are commonly used to determine algae species and estimate cell abundance for colonial and filamentous cyanobacteria. The outcomes are frequently specified as cell mL-1 and can be later used in the Alert Levels Framework to evaluate the reservoir in terms of cyanobacterial load.

Based on this information, it is possible to implement analytical techniques suitable for determining toxin levels. Another method of detecting cyanotoxins are real-time monitoring programs that collect water quality parameters, such as Phycocyanin. This way, water managers can receive early warnings of toxic cyanoHABs.

Treatment for cyanobacterial blooms

CyanoHABs cause significant challenges for environmental management of water bodies.
Ensuring the healthy functioning of water ecosystems and the safety of recreational activities requires effective management of cyanoHABs.

There are various methods to treat cyanoHABs, including physical removal, chemical procedures, biological inactivation, and ultrasonic control.

Chemical treatment

Chemical treatment is the most common treatment method, and also the most damaging to the environment. It involves using copper sulfate and hydrogen peroxide, which cause sudden death or lysis of cyanobacterial cells. Massive amounts of cyanotoxins are being released back into the water. Chemical intervention does not resolve the core problem of cyanoHABs, which reappear after treatment.

Nutrient reduction

Reducing the nutrient loading entering our water systems could help limit the cyanoHAB growth. However, this requires radical changes in urban, agricultural, and industrial activities – the main nutrient pollution producers. Sources of nutrient pollution include agriculture, aquaculture, animal farming, wastewater, stormwater, fossil fuels, and households. This great variety of sources makes nutrient pollution tremendously difficult to control as quickly and effectively as necessary.

Ultrasonic control

To avoid using harmful chemicals and achieve a fast and effective treatment, LG Sonic has developed an ultrasound technology to manage algal blooms. This ultrasonic system creates a sound barrier on the top layers of the water to control the growth of cyanobacteria. Under such conditions, cyanobacteria cannot reach the water surface, so it cannot keep growing. To maintain the ecological balance, the technology does not eliminate cyanobacteria; it reduces them by up to 90%. This way, the water ecosystem is safely restored by maintaining healthy levels of cyanobacteria.


Successful mitigation of cyanoHABs must rely on an in-depth understanding of the principles of aquatic ecosystem dynamics. It must be based on reliable surveillance, alerts, eco-friendly treatment methods, and adequate action plans. Inadequate mitigation of cyanoHABs leads to serious damage to aquatic ecosystems. This can cause significant socio-economic losses that can be even worse than the impacts of toxic cyanobacterial blooms.