The sub-tropical climate in Namibia, together with nutrients in the water, creates a good environment for phytoplankton, especially cyanobacteria. Many of these produce toxins that can be harmful to people and animals. One of the algal toxins is microcystin. This toxin is hepatotoxic, i.e. the primary toxic effect is on the liver. Cases of gastro-enteritis, nausea, vomiting, diarrhoea, muscle weakness and paralysis have been associated with the consumption of water containing high numbers of blue-green algae all over the world.

The aim of this study was to chart the possible linkages between algae toxins in drinking water and related illnesses in Windhoek. The results showed an annual seasonal variation in gastrointestinal problems and high levels of liver-enzymes. It also showed a relationship between the concentration of chlorophyll-a in the drinking water and the cases of people suffering from diarrhoea.