Over the years, cash crop plantations have grown in size and number. Agricultural chemicals, applied on these plantations are washed into rivers during the rainy season, and end up in the lake, providing nutrients for unwanted, unsightly algal blooms. The plantations attracted migrant workers who settled in the area. As the population grew and fishing methods advanced, overfishing became a problem and catch sizes began to drop. Cichlid numbers had fallen drastically, comprising only 1 per cent of fish weight, while those of the Nile perch had suddenly jumped to constitute 80 per cent.
Cichlids are small bony fish whose mouth parts have evolved to suit their different eating patterns.
Some feed on fish eggs, others on insects, while a majority prefer detritus. With the absence of significant fish numbers to feed on detritus, the organic material decays, consuming oxygen as it sinks to the floor. Some areas of the lake, particularly the lowest levels, are depleted of oxygen and are thus inhabitable. They appear to be dead zones. For decades, ecologists have travelled to Lake Victoria to study cichlids for their explosive evolutionary capabilities.