Harare's water supply under threat

A recent study has highlighted a rising environmental threat to Harare's primary water source, Lake Chivero, with increasing algal growth potentially compromising the capital city's water quality and ecosystem. The study, conducted by Muongeni Manda, a postgraduate researcher at Chinhoyi University of Technology, was presented at the Aeronautical Congress in Milan, Italy.

Manda's research, which examined the water extent and quality of Lake Chivero from 2017 to 2023, found that higher nutrient concentrations in the lake - primarily nitrogen and phosphorus - are fueling a process known as eutrophication. This condition, characterized by excessive nutrients, is contributing to the growth of harmful algal blooms, which can degrade water quality and harm aquatic life by depleting oxygen levels.

"Lake Chivero's water quality is declining due to increased levels of nutrient concentrations, including nitrogen and phosphorus, a condition known as eutrophication," Manda explained. "This leads to algal blooms that degrade the water quality and aquatic life, with the cause likely being urbanization and agricultural activity."

The study used advanced remote sensing technologies, including Digital Earth Africa's Modified Normalised Difference Water Index (MNDWI) and Normalised Difference Chlorophyll Index (NDCI), to track changes in water extent and chlorophyll-a concentration. These tools enabled Manda to track the extent of algal growth and its potential impact on the lake's oxygen levels, with concerns about oxygen depletion and fish deaths emerging as serious risks.

The report also noted that urbanization, agricultural runoff, siltation, and the spread of the invasive water hyacinth are exacerbating the situation. The presence of the water hyacinth, a fast-growing aquatic plant, is particularly problematic as it clogs waterways and outcompetes native plant species, further destabilizing the lake's ecosystem.

"Extra water from rainfall can dilute the salinity and alkaline levels of the lake, creating a less hospitable environment for algae and reducing the food source for flamingos," Manda added. "Where water extent and chlorophyll concentration have both increased, it is likely that rainwater has washed additional nutrients into the lake, boosting algal growth."

Kenneth Mubea, a Digital Earth Africa representative, emphasized the importance of addressing these environmental concerns to protect both the lake's ecosystem and Harare's water supply. "Manda's findings are crucial in understanding how we can protect Lake Chivero's habitat and the city's water source," Mubea said. "It's vital that we tackle these issues before they lead to irreversible damage."

Experts warn that if left unchecked, the ongoing algal blooms could have disastrous consequences for Harare's water supply, already under strain due to pollution, urban growth, and invasive species. Lake Chivero, located on the Manyame River downstream from Harare, serves as the primary source of water for the city and is also crucial for irrigation, fishing, and bird habitats.

The lake is home to a delicate ecosystem, with shoreline vegetation and aquatic life that are vulnerable to seasonal fluctuations in water levels and water quality. As the threat of algal blooms grows, the future of Harare's water supply and the health of the surrounding environment are increasingly at risk.