Harare- A parliamentary inquiry has revealed that Lake Chivero, Harare’s primary water source, is experiencing “severe ecological shocks” including massive fish die-offs and the rapid proliferation of invasive water hyacinth, driven by catastrophic levels of pollution from raw sewage.

The Portfolio Committee on Environment, Climate and Wildlife’s report, chaired by Sam Matema who is also the Member of Parliament for Buhera Central in Zimbabwe confirmed a devastating portrait of an ecosystem in collapse. The committee’s analysis of environmental data from 12 monitored rivers between 2013 and 2024 confirms “severe chemical and biological contamination” that is destroying aquatic life and threatening the region’s water security.

Lake Chivero is a reservoir on the Manyame River, situated downstream from Harare and its surrounding settlements. It provides the main water supply for the capital and is used for irrigation, fishing, and serves as a habitat for birds and wildlife.

The lake is home to a delicate ecosystem of shoreline vegetation and aquatic life, including fish, invertebrates, and plankton. It also includes the surrounding Miombo Woodlands that provide habitat to various local animal species, including white rhino, plains zebra, ground pangolins, and numerous bird species.

However, over the years, the lake has faced mounting ecological threats. Research presented at the Aeronautical Congress in Milan, Italy, by Muongeni Manda, a postgraduate researcher at Chinhoyi University of Technology, analysed Lake Chivero’s water extent and quality between 2017 and 2023. Her findings indicate increasing nutrient concentrations, leading to eutrophication and detrimental algal blooms.

“Lake Chivero’s water quality is declining due to increased levels of nutrient concentrations, including nitrogen and phosphorus, a condition known as eutrophication,” Manda said. “This results in algal blooms degrading the water quality and aquatic life by depleting oxygen in the water. The cause is likely to be urbanisation and agricultural activity”.

The parliamentary committee’s scientific data reveals a water system in crisis. Dissolved oxygen averages 51.2%, below the 60% threshold needed to support aquatic life.

This depletion is driven by organic overloading from raw sewage that leaks into major river systems like the Manyame and Mazowe. Biological oxygen demand averages 9.48 mg/L, four to five times higher than acceptable limits. This elevated demand is “a critical indicator of excessive organic waste, largely from raw or partially treated sewage, which consumes available oxygen as it breaks down, resulting in massive fish kills at Lake Chivero.”

Phosphate levels average 0.79 mg/L, causing widespread eutrophication. High concentrations trigger “the rapid, out-of-control growth of algae, creating a thick green scum on the surface that suffocates water bodies like Lake Chivero by blocking light and oxygen.” Turbidity averages nearly 30 NTU, six times higher than the healthy limit. High turbidity indicates dangerous concentrations of suspended solids that “block sunlight from reaching aquatic plants and cause physical damage to fish gills.”

The committee’s spatial analysis is damning. “The highest concentrations of phosphates are clumped directly around urban centres, proving that the primary source of this pollution is the leakage of raw or poorly treated waste from overwhelmed municipal wastewater systems into the Manyame, Mazowe and Save river systems.”

The ecological damage extends beyond fish kills. In 2024, the Zimbabwe Parks and Wildlife Management Authority confirmed the deaths of four rhinos, three zebras, four wildebeest, and four fish eagles, all attributed to pollution-related causes.

The report also documents invasive water hyacinth proliferation on Lake Chivero, further disrupting the delicate balance of the local ecosystem. Massive algal blooms have appeared on rivers such as the Sebakwe.

“The pollution of Lake Chivero has had serious ecological and environmental consequences over the years,” said the Environmental Management Agency (EMA) spokesperson Amkela Sidange. “This has resulted in algae blooms that deplete oxygen levels in the water, making it difficult for aquatic organisms to survive. The pollution has the potential to result in the decline of fish species, significantly due to oxygen depletion, habitat loss and high toxin concentrations”.

The ecological collapse of Lake Chivero is not merely an environmental tragedy. It is a direct threat to the water security of millions of people who depend on the lake for drinking water. The report notes that the contamination of primary water sources has “directly contributed to recurring outbreaks of waterborne diseases.”

Harare uses up to 10 different water treatment chemicals and spends an average of US$1.5 million per month on water treatment, highlighting the growing cost of supplying clean water amid rising contamination levels.

The committee recommends urgent funding for the “bio-remediation of Lake Chivero” by 31 December 2026, to “deploy immediate biological measures to clean the water source, counter the high levels of phosphates and excessive organic waste that cause massive fish kills, and eradicate the invasive water hyacinth.”

The report also calls for the national Environmental Fund to be “robustly capitalised” to provide a financial backstop for the restoration of ecological hotspots where “environmental damage has exceeded municipal uphold their statutory duty to protect both citizens and public natural resources.”