Serious cases of pollution have also been detected from water samples taken from the Manyame and Hunyani rivers.
According to the research, Lake Chivero is highly eutrophic and levels of nutrients in the water are now very high because of raw effluent, domestic and industrial waste being discharged into it, resulting in blue-green algae blooms and water hyacinth.
University of Zimbabwe Department of Biology lecturer and researcher, Dr Maxwell Barson said accumulation of ammonia and inorganic pollutants among other chemicals have become much higher than before in the lake, adding that such nutrients become more concentrated during periods of droughts when water levels are low.
â€œWe have not yet ascertained if the overall levels of weed growth nutrients such as phosphates, nitrates, potassium and sewage effluent are still within acceptable limits according to World Health Organisation (WHO) standards for drinking water and Zimbabwe waste effluent standards,â€ said Dr Barson.
Dr Barson said the Lake Chivero pollution could be reduced by strict enforcement of trade and waste effluent regulations and by imposition of stiff penalties to those who do not comply.
He also said as a way forward, authorities can use the integrated lake basin management to rehabilitate the lake or divert sewage effluent somewhere else away from Lake Chivero catchment area to a special dam where water could be separately treated for industrial usage or irrigation.
Lake Chivero was built in 1952 as the principal water supply for the City of Harare.
It is located downstream from the city which discharges sewage into two of its tributaries, the Mukuvisi and Hunyani Rivers.
The growth of Harareâ€™s population has not been matched by infrastructure expansion thus exerting pressure on pipes which are regularly bursting.