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The advancing onslaught of toxic red algae blooms in our freshwater systems

Anthony Turton
By Anthony Turton
23 Jul 2024
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E. sanguinea produces a potent toxin that disables fish. The toxin causes disorientation, asphyxiation, and the inability to swim in an upright position. But perversely, it does show promise in the treatment of cancer.

It is a well-known fact that South African rivers are in poor health. The Green Drop report paints a woeful picture of neglect. One of the major drivers of this process is enrichment of the water by nutrients – typically phosphate and forms of nitrogen such as ammonia – all of which is well documented in scientific literature that the average citizen will never read.

Society seems to have shrugged this off as somehow being the new normal. The average person seems to accept that rivers and lakes are green, with little regard for the implications.

But what if those rivers suddenly began to flow blood red? Would this change public perceptions in any way?  

The African Journal of Aquatic Sciences is a prestigious scientific journal. It is a custodian of new knowledge in the aquatic science community, so when it publishes something that is out of the ordinary, it is wise to take note.

In 2021, Professor Sanet Janse van Vuuren and Dr Anatoliy Levanets, both from North-West University, published a paper that reported blooms of an unusual cyanobacteria named Euglena sanguinea Ehrenberg in different parts of South Africa.

Not usually present


What made this observation important were two facts. Firstly, E. sanguinea is not usually present in South Africa, so this is an important observation on its own. Intensive literature searches indicate that this species was sparsely reported throughout Africa, with only one previous record in South Africa.

Secondly, this species of blue-green algae can manifest as red under certain conditions. While red tides are well known in seawater, they are infrequent in freshwater.

In 1832, E. sanguinea was first described in the literature by Ehrenberg as one of the few autotrophic organisms that had the capacity to turn freshwater red. An autotrophic organism is one that can convert inorganic substances like carbon dioxide, water and other chemicals into food that can sustain its own life form.  

In fact, E. sanguinea is the most-found freshwater alga capable of turning the water red. The name says it all, because in Latin the word for blood is sanguis.

It is widely reported in the scientific literature that this species favours conditions of elevated temperatures, a slightly acidic pH, with high nitrogen and phosphate availability and strong sunlight. It is these precise conditions that now prevail in many of our rivers and dams in South Africa, largely the result of sewage return flows and acid mine drainage.

The red colouration is an interesting survival strategy that we can learn many lessons from. Ultraviolet light is a natural steriliser, destroying DNA, and therefore killing organisms exposed to such light.

A natural form of  sunblock


However, the red cyanobacteria can synthesise a natural form of sunblock, known as haematochrome. Once again, the word “haemato” refers to blood. This protection apparently comes from the ability of the organism to synthesise a substance known as astaxanthin, a red pigment now farmed commercially in Australia and used as a health supplement.

It was this ability to survive the UV radiation bombarding Earth billions of years ago, before our oxygen-based atmosphere had been formed, that gave these creatures their ability to survive. It is for this reason that they are called extremophiles because their very presence is an indicator of conditions hostile to more familiar life forms. 

Commercial astaxanthin production as a human health supplement in Queensland Australia. (Photo: Anthony Turton)



Despite possible health benefits from potentially harvesting astaxanthin, E. sanguinea also produces a potent toxin that disables fish. In commercial fish farming operations in the US, the presence of the toxin caused disorientation, asphyxiation, and the inability to swim in an upright position.

The active ingredient was extracted and isolated where it was initially identified as a new-to-science toxin named euglenophycin. This was found to be chemically like the toxin produced by fire ants. However, the discovery opened a new frontier of research for cancer treatment, because euglenophycin was believed to be capable of reducing blood flow sufficiently to inhibit cancer formation.

Related to this discovery was a surprise from an environmental management perspective, because it was shown that euglenophycin can inhibit the growth of Microcystis. This has major implications for South Africa, because Microcystis is a dominant genus of cyanobacteria found in almost all our sewage-enriched dams. These creatures produce a potent toxin known as microcystin.    

Given the relative rarity of E. sanguinea, it is interesting to note that the first recorded case in South Africa was in 1977 when it was found to be a dominant species in a sewage maturation pond.

Read more: From finance to forestry and fisheries – South Africa’s new environment minister takes a pragmatic approach

It was subsequently reported in 2016 in Mpumalanga, and again in 2020 in Limpopo. The paper published in the African Journal of Aquatic Sciences in 2021 noted that the red coloration is determined by environmental factors, most notably light intensity, so colonies can also be present in green forms.

Doctors Janse van Vuuren and Levanets noted in their conclusion that this species is problematic because it produces scum, and can be toxic and cause taste and odour problems in water contaminated with the toxin euglenophycin.

It is for this reason that the recent bloom of E. sanguinea at Pecanwood Estate adjacent to the Hartbeespoort Dam is of public interest. The recent presence of the organism in Hartbeespoort Dam in low numbers is known to aquatic scientists, but the population density was so low as to be insignificant.

But then, in May 2024, an ornamental dam on Pecanwood Estate suddenly turned red. This is a well-managed residential estate, with a competent environmental management team keeping the constructed wetlands in an aesthetically pleasing and functional condition.

This bloom was captured on camera by Gill Ledger, known for her meticulous recording of all microorganisms found in the constructed wetland systems used to manage the eutrophic waters from the dam. She reached out to professional scientists and confirmed the identity of E. sanguinea as the culprit.

During May 2024, the first blooming of E sanguinea was recorded at Pecanwood Estate on the banks of Hartbeespoort Dam. (Photo: Gill Ledger)



The latest blooming event confirms the points raised in the African Journal of Aquatic Sciences paper, because the dominant species of cyanobacteria in the Hartbeespoort area has always been Microcystis, which could possibly be displaced by its red rival. This event also raises the spectre of rivers flowing red as a distinct possibility in different parts of South Africa over the next decade.

The reported presence of E. sanguinea confirms that our aquatic ecosystems are changing. Everything we know about them in their present state might be turned on its proverbial head soon if that rate of change exceeds our institutional capacity to cope.

The role of citizen science is also highlighted by this case, because the environmental management team at Pecanwood Estate is doing an excellent job of networking with professional scientists and non-governmental organisations.

Positive engagement


We need more of this positive engagement as we are confronted by the relentless onslaught of hyacinth, water lettuce and cyanobacteria, all responding to the ideal conditions created by a warming planet and increased flows of sewage effluent and acidic mine water into our rivers and dams.

As a nation we must insist that more of our taxes are invested into the science, engineering and technology needed to keep us safe in a rapidly changing world.

In closing, this is a call to our entrepreneurs in South Africa. If the Australians can produce astaxanthin from red algae, then why can’t we do the same? Where is the plan for an astaxanthin production facility located in the industrial park adjacent to Hartbeespoort Dam?

Where is the biomedical research proposal to better understand the cancer inhibition properties of euglenophycin? DM

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