By Johnson Siamachira
Harare, (New Ziana) — Peter Muronzi, a seasoned fisherman at Gache Gache Fishing Camp along the shores of Lake Kariba, has watched helplessly as his daily catch has dwindled over the years.
“Every year, it gets harder to find healthy fish,” he laments, reflecting a growing crisis that threatens not only his livelihood but the entire ecosystem surrounding one of Africa’s largest man-made lakes.
The ecological balance of Lake Kariba hangs by a thread, primarily due to rampant fish diseases fuelled by parasites and worsened by pollution from sewage, mining, and agricultural waste. As fish reproduction falters, yields plummet, prompting concern among local fishermen and environmentalists alike.
Parasites, including nematodes and cestodes, wreak havoc on fish populations in Lake Kariba. Areas near sewage discharge points report higher disease prevalence, a direct consequence of deteriorating water quality. “Compromised water quality harms fish gills and other sensitive organs, making them more susceptible to diseases and impacting their growth and reproduction,” says Dr. Lightone Marufu, an aquatic ecologist at the University of Zimbabwe(UZ)’s Biological Sciences and Ecology Department.
Dr Marufu is also the Department’s representative at the University of Zimbabwe Lake Kariba Research Station.
Fish disease expert Dr Nyasha Mabika, also from the same UZ department, has reported on rampart fish parasites, particularly those affecting the popular sport fish, Tigerfish, which is not only of economic value to local fishery communities in Kariba but also to the tourism sector in the country through hosting the Kariba International Tiger Fishing Tournament, held annually in October. Bringing together both local and international competitors, the tournament has been held every year since 1962.
Dr. Marufu underscores the role of climate change in exacerbating these issues. “Climate change can trigger disease outbreaks by altering water quality and availability. Changes in temperature and irregular water inflow and outflow can disrupt entire ecosystems,” he cautions. He warns that without effective mitigation strategies, both biodiversity and the livelihoods dependent on Lake Kariba stand to suffer significant losses.
The interplay between the lake and its surrounding environment is crucial. “What happens in any water body is also a result of what is happening around it, particularly its catchment,” Dr. Marufu says. Population growth and development projects in the area bring both opportunities and challenges. While increased development can stimulate economic growth, it can also lead to increased pollution if not carried out in a sustainable and environmentally-friendly way. “We need upgraded waste management in Kariba town to cope with the pressures of a growing population,” he says.
The consequences of fish diseases extend far beyond the water’s edge. Local fishing communities, many of which rely on fish trade for their income, face economic uncertainty as reports of diseases or invasive species trigger panic. “When disease scares emerge, families worry about the quality of their catch and potential market losses,” says Elmon Dhlomo, chief technician at the UZ Lake Kariba Research Station. “But they are quick to cooperate with researchers and government agencies to ensure their livelihoods are sustained.”
Invasive species pose another layer of threat. Australian redclaw crayfish, for example, not only consumes local fish but also damage catches while ensnared in fishing nets, according to research studies by Dr Marufu and Dr Takudzwa Madzivanzira (also from University of Zimbabwe’s Biological Sciences and Ecology Department). Their research findings indicate that these invaders disrupt the natural ecosystem, degrade biodiversity, and can ultimately jeopardise human health and livelihoods.
Dr Marufu also says that there was evidence of harmful parasites being associated with the invasive crayfish. These parasites might jeopardise the health of fish not only in Lake Kariba, but other national water systems. He emphasises the need to prevent the introduction of such species into the nation’s other aquatic systems without prior environmental impact assessments and informed approval (or not) from relevant governmental authorities.
To combat some of these challenges, the University of Zimbabwe through its Lake Kariba Research station and experts from its Biological Sciences and Ecology Department (Faculty of Science) collaborates with government agencies and other key stakeholders to monitor fish diseases, invasive species, and water quality. Since the lake’s construction in the 1950s, research findings have raised awareness of potential threats to fish and community livelihoods.
As Lake Kariba grapples with multifaceted challenges, the need for ongoing research and community engagement becomes increasingly evident. The health of this vital waterway and the well-being of its local populations depend on proactive measures and informed responses to the threats at hand.
In the end, the fate of Lake Kariba—and the livelihoods of those like Peter Muronzi—rests on collective ability to address the complex issues that threaten its ecological biodiversity. Without decisive action, the lake may not only lose its vibrant fish populations but also the vital connections that sustain its surrounding communities.
New Ziana
