As climate change leads to rising temperatures and shifting weather patterns around the world, scientists are increasingly concerned about the impact these changes will have on ecosystems, particularly freshwater bodies. One area of concern is the proliferation of harmful algal blooms (HABs), which can have significant ecological, economic, and health consequences. A particularly harmful type of HAB is driven by cyanobacteria, a diverse group of microorganisms that thrive in nutrient-rich, warm waters. These blooms not only reduce water quality but also produce toxins that pose threats to wildlife, livestock, and human populations who rely on the water.
A unique study, led by University of Michigan scientists, has extended the understanding of how cyanobacterial blooms form and evolve under the influence of climate change in Lake Victoria’s Winam Gulf, a region plagued by year-round harmful algal blooms. The findings, which have implications for Lake Erie in the United States as it also faces warming temperatures and increasing cyanobacterial activity, contribute significantly to our knowledge of cyanobacterial genetics and its harmful effects on ecosystems and public health.
Cyanobacteria and Harmful Algal Blooms
Cyanobacteria, also known as blue-green algae, are naturally occurring microorganisms in lakes, rivers, and oceans. Under favorable conditions—such as elevated temperatures and nutrient pollution—these bacteria can proliferate, forming dense clusters known as cyanobacterial harmful algal blooms (cyanoHABs). These blooms can discolor water, cause fish kills, and release harmful toxins into the environment. These toxins can enter the food chain and pose risks to both animal and human health.
Winam Gulf, a semi-enclosed embayment in Lake Victoria, is a critical area for both environmental research and local livelihoods. As the site of Kenya’s third-largest city, Kisumu, Winam Gulf is vital to the local community, which relies on fishing and agriculture for sustenance. However, the year-round presence of cyanobacterial blooms presents a growing threat to public health and economic stability.
The Study: Understanding Cyanobacterial Composition in Winam Gulf
One of the key challenges in managing cyanobacterial harmful algal blooms is the ability to track the organisms responsible for the blooms and the toxins they produce. In the case of Winam Gulf, despite decades of bloom activity, no comprehensive genetic survey of cyanobacteria had been performed before this study. As a result, local authorities lacked detailed information about the species involved in the blooms and their potential for toxin production.
In collaboration with scientists from North America and Kenya, the researchers from the University of Michigan and Bowling Green State University performed a genetic survey of the cyanobacteria present in Winam Gulf. Sampling took place during 2022 and 2023, covering a variety of sites within the gulf to capture a complete picture of the microbial composition of the region.
The team discovered that the dominant bloom-forming cyanobacteria in the gulf was Dolichospermum, a species commonly found in cyanobacterial blooms. In addition to Dolichospermum, the researchers found other cyanobacteria such as Microcystis and Planktothrix—two species frequently associated with harmful blooms in other regions, including Lake Erie in the United States. The presence of these species in Winam Gulf highlighted a striking similarity between the conditions in the Kenyan water body and those in other parts of the world facing similar water quality challenges.
What made the findings particularly important was the observation of elevated cyanobacterial growth in areas characterized by high turbidity—waters with suspended particles from inflowing rivers. In turbid waters, the blooms were often not visible to the naked eye, masking the signs of contamination. This aspect posed a serious risk to communities using untreated water from the lake, as they could unwittingly consume contaminated water without recognizing the harmful algal blooms.
Genetic Sequencing and Toxin Production
By sequencing the DNA of the cyanobacteria, the researchers were able to identify not only the dominant species present but also the genetic makeup that enables these cyanobacteria to produce toxins. In particular, the researchers focused on Microcystis, a cyanobacterium known for producing a potent liver toxin called microcystin. This toxin can cause severe health problems in humans and animals, such as liver damage, gastrointestinal distress, and, in extreme cases, death.
Lauren Hart, lead author of the study and a doctoral student at the University of Michigan, said, “Microcystis has been shown to produce more than 300 gene clusters involved in the production of various molecules, both toxic and non-toxic. This genetic catalog is crucial for understanding the capacity of Microcystis and other cyanobacteria to produce a broad range of harmful compounds, some of which have never been identified before.”
The work highlights the importance of using advanced techniques like environmental genomics to unravel the genetic potential of harmful cyanobacterial species. By identifying which cyanobacteria are capable of producing harmful toxins and other potentially harmful compounds, researchers can improve monitoring efforts and develop more effective strategies for managing water resources in regions vulnerable to HABs.
Public Health Concerns
Harmful cyanobacterial blooms not only endanger aquatic life but also pose serious health risks to humans. Toxins produced by cyanobacteria can enter the human body through multiple routes, including ingestion of contaminated drinking water, inhalation of airborne toxin-laden droplets, and dermal exposure while swimming or performing household chores such as laundry. The most serious health effects are associated with the ingestion of cyanotoxins, particularly microcystins, which can lead to liver damage, stomach cramps, diarrhea, and nausea.
Kisumu and its surrounding areas have a high prevalence of health conditions such as malaria and HIV/AIDS. This makes the population more vulnerable to the harmful effects of cyanobacterial toxins, particularly for individuals who are immunocompromised. For many people in the region, boiling contaminated water is the standard practice for making it safe to drink. However, boiling water contaminated with cyanobacterial toxins is ineffective and could make the situation worse, as the process can break open cyanobacteria cells, releasing even more toxins into the water.
“The health risks are particularly concerning in Kenya because there are no water treatment plants like those available in the United States to remove cyanobacterial toxins,” explained Dr. George Bullerjahn, senior author of the study and professor of biological sciences at Bowling Green State University. “Rural populations are more likely to drink untreated lake water directly, and they face significant exposure risks that people in developed countries rarely encounter.”
In response to these risks, researchers emphasized the importance of educating local communities about the dangers posed by harmful algal blooms, especially during peak bloom periods when the presence of toxins in water sources is highest. Informing residents about how to identify cyanobacterial blooms and how to adapt their water use could help mitigate some of the risks associated with exposure.
Addressing Synergies Between Cyanotoxins
In addition to the study’s focus on the identification of individual toxins produced by cyanobacteria, researchers, including Hart, are also investigating the potential for synergies between different cyanotoxins. Hart has become particularly interested in understanding whether the combined exposure to multiple toxins may amplify their harmful effects. Specifically, she is exploring how two toxins from Microcystis—microcystin and another unidentified toxin—might interact within the human body, potentially intensifying their effects.
Hart’s work on this issue aims to advance the understanding of how different types of toxins interact and whether exposure to them simultaneously could result in amplified risks, such as liver damage and disruption of the gut microbiome. This line of research is particularly significant given the high rates of immunocompromised individuals in Kisumu, where people living with HIV or other conditions might experience heightened vulnerability to toxin exposure.
Implications for Lake Erie and Future Climate Models
While this research primarily focuses on the Winam Gulf of Lake Victoria, the findings have profound implications for other freshwater ecosystems affected by warming temperatures and nutrient pollution—such as Lake Erie. Lake Erie is known for its recurrent harmful algal blooms, driven in part by warming temperatures, nutrient-rich agricultural runoff, and urban pollution. The study’s revelations about the genetic diversity of cyanobacteria in Lake Victoria, the toxins they produce, and the risks posed to local populations can serve as an important model for understanding how these same patterns might emerge in other lakes affected by similar environmental pressures.
Conclusion
The study of cyanobacterial harmful algal blooms (cyanoHABs) in Kenya’s Winam Gulf provides valuable insights into the broader global challenge posed by these blooms, particularly in the context of a warming climate. The research highlights the genetic diversity of cyanobacteria, the toxins they produce, and the risks to both public health and the environment. With similar conditions observed in Lake Erie, the findings offer a crucial model for understanding how harmful algal blooms may evolve in other freshwater systems. As climate change continues to drive temperature increases and nutrient pollution, the need for effective monitoring, community education, and improved water management strategies becomes ever more urgent. By addressing the risks of cyanotoxins and their potential synergistic effects, the study underscores the importance of proactive solutions to safeguard public health and preserve freshwater ecosystems globally.
Reference: Lauren N. Hart et al, Metagenomics reveals spatial variation in cyanobacterial composition, function, and biosynthetic potential in the Winam Gulf, Lake Victoria, Kenya, Applied and Environmental Microbiology (2025). DOI: 10.1128/aem.01507-24