The 2020 elephant deaths in the Okavango Delta should serve as a wake-up call for the urgent need for preventive action. This feature explores the biochemistry behind cyanobacterial blooms, real-world case studies of their deadly impact and strategies to mitigate their risks
DOUGLAS RASBASH
Special Correspondent
In recent years, Botswana has faced a series of alarming environmental and socio-cultural events with profound implications for public health, biodiversity and the economy. Among the most pressing threats are harmful algal blooms (HABs) caused by cyanobacteria – microscopic organisms capable of producing potent toxins that jeopardise life across the spectrum.
Most notably, the unexplained deaths of over 330 elephants in the Okavango Delta in 2020 turned global attention to the dangers of these blooms, but the risks extend far beyond elephants. Cyanobacterial toxins pose a serious threat to communities, wildlife and water security in Botswana. This feature explores the biochemistry behind cyanobacterial blooms, real-world case studies of their deadly impact, and strategies to mitigate their risks, urging Botswana’s decision-makers and high-risk communities to take immediate action. But what are cyanobacterial blooms?
Cyanobacteria, also known as blue-green algae, are photosynthetic microorganisms that thrive in water. While naturally occurring, they can proliferate explosively under certain conditions, forming harmful algal blooms (HABs). These blooms often appear as scum or discolouration on the water’s surface and release toxins into the water and air.
The proliferation of cyanobacteria is closely linked to environmental factors. Nutrient pollution from runoff containing nitrogen and phosphorus from agriculture and untreated sewage acts as a fertiliser for cyanobacteria. Warmer water temperatures accelerate their growth, as does water stagnation. Reduced flow in water bodies creates the perfect breeding ground for these blooms.
Cyanobacteria’s biochemistry enables them to dominate aquatic ecosystems. They possess unique pigments to capture light efficiently and produce gas vesicles to control buoyancy, allowing them to access nutrients and light at different water depths. However, their most insidious trait is their ability to produce cyanotoxins, which can harm or kill animals and humans upon exposure.
The Danger of Cyanotoxins
They are secondary metabolites that cyanobacteria release into their environment. These include: Microcystins: These toxins target the liver, causing acute or chronic liver damage. They are known tumour promoters and have been linked to cancers in long-term exposure. Potent neurotoxins mimic neurotransmitters, leading to overstimulation of the nervous system and respiratory failure.
Cylindrospermopsins disrupt protein synthesis, damaging the liver and kidneys. Saxitoxins block sodium channels in nerve cells, causing paralysis and even death. When cyanobacterial blooms occur, these toxins can accumulate in water, fish and even the air, posing risks to all who depend on the water source.
The Impact of Cyanobacterial Blooms
The Okavango Delta Elephant Deaths (2020)
In a tragic event that shocked Botswana and the world in 2020, over 330 elephants mysteriously died in the Okavango Delta. Early investigations ruled out poaching, anthrax and infectious diseases. Eventually, scientists identified anatoxins produced by cyanobacteria as the culprit. Elephants, which require large amounts of water daily, likely drank from or bathed in stagnant waterholes contaminated with cyanobacteria. The neurotoxins caused paralysis and respiratory failure, leading to sudden deaths.
This event was not an isolated incident but a warning sign of the broader environmental challenges that Botswana faces. Droughts, higher temperatures, and nutrient pollution have created conditions where toxic blooms are becoming more frequent, threatening not just elephants but entire ecosystems.
Human Health Risks
Risks to human health, such as in Lake Taihu, China in 2007, are also possible. Although not in Botswana, the crisis in Lake Taihu demonstrates the human impact of cyanobacterial blooms. A massive bloom contaminated the drinking water supply for two million people, leading to widespread gastrointestinal illnesses and disruptions in daily life.
The event underscored the importance of clean water infrastructure and proactive monitoring.
Similarly, the Darling River in Astralia (1991) saw a bloom spanning over 1,000 kilometres that killed livestock and contaminated water supplies. It highlighted the vulnerability of arid regions where water stagnation and nutrient loading are common – a scenario increasingly mirrored in Botswana’s dry seasons.
Botswana is particularly vulnerable to cyanobacterial blooms and their effects. Climate change and concomitant rising temperatures and prolonged droughts have increased the frequency of water scarcity and stagnant water sources where cyanobacteria thrive. Furthermore, fertiliser runoff from farming areas contributes to nutrient overload in rivers and reservoirs.
Both humans and wildlife in Botswana rely heavily on limited water sources, increasing the likelihood of exposure to contaminated water. Areas like the Okavango Delta and Chobe National Park are rich in wildlife, but the concentration of animals around waterholes during dry seasons amplifies the risks of mass die-offs.
The death of keystone species like elephants disrupts ecosystems, affecting everything from vegetation growth to predator-prey dynamics. The loss of biodiversity can also hurt Botswana’s ecotourism industry, which is a significant contributor to the economy.
Public health concerns arise because cyanotoxins are not just an ecological issue but a public health hazard. Communities that rely on untreated water sources are at risk of gastrointestinal, liver and neurological illnesses. Chronic exposure can lead to long-term health consequences, including cancer.
Economic costs addressing cyanobacterial blooms requires significant resources for water treatment, health interventions, and ecosystem restoration. For a country already facing economic challenges, these costs could be crippling without preventive measures.
What Can Be Done?
Proactive strategies are essential to mitigate the risks of cyanobacterial blooms. In keeping with our remit to inform, The Botswana Gazette offer a set of recommendations for Botswana’s decision-makers and at-risk communities:
- Strengthening Water Quality Monitoring: Establish regular testing for cyanotoxins in water bodies, especially during peak bloom seasons. Deploy rapid detection technologies such as enzyme-linked immunosorbent assays (ELISA) for early intervention.
- Reducing Nutrient Pollution: Implement stricter regulations on agricultural runoff by promoting the use of environmentally-friendly fertilisers. Upgrade wastewater treatment plants to reduce phosphorus and nitrogen discharge into rivers and reservoirs.
- Managing Water Resources Design: Managing water resources design and maintaining artificial waterholes with deeper, cooler water to deter cyanobacteria growth is important. Restoring natural water flows in rivers and wetlands to reduce stagnation would also help a great deal.
- Public Awareness Campaigns: Educate communities about the risks of drinking untreated water during blooms. Encourage the use of filters or alternative water sources in high-risk areas.
- Wildlife Conservation Measures: Monitor wildlife health for signs of cyanotoxin exposure. Create safe water points for animals during droughts to minimise reliance on contaminated sources.
- Long-Term Climate Adaptation: Invest in renewable energy and sustainable agricultural practices to address the root causes of climate change, which exacerbates bloom conditions. Collaborate regionally to share knowledge and resources for combating HABs.
Botswana’s unique position as a biodiversity hotspot and water-scarce nation makes it particularly vulnerable to the dual threats of climate change and cyanobacterial blooms. The 2020 elephant deaths in the Okavango Delta should serve as a wake-up call to the urgent need for preventive action. Decision-makers must prioritise investments in water quality monitoring, pollution control, and public education to safeguard both human and ecological health.
Communities, especially those in high-risk areas, must remain vigilant and advocate for policies that protect their water sources. By addressing the underlying causes and consequences of harmful algal blooms, Botswana can turn the tide on this growing threat and secure a healthier, more resilient future for all.
Here are sources that address water quality guidelines and related health topics:
WHO: Guidelines on Recreational Water Quality
WHO: Health Aspects of Recreational Water Use
WHO Newsroom: Updates on Water, Sanitation, and Hygiene