| Abstract: | Beginning in the mid‐1980s Lake Victoria experienced severe eutrophication and it was suggested that deteriorating water quality might lead to a collapse of its fisheries. A series of lake‐wide surveys carried out 1999–2001 and 2005–2009 revealed that the temperature of the lake had risen by > 1 °C since 1927, with more rapid warming of the deeper waters reducing the thermal gradient in the water column and thus weakening stratification and the extent and severity of deoxygenation. The chlorophyll a concentrations in open water decreased since the 1980s, while Secchi disc visibility increased, indicating a reduced severity of algal blooms. Chlorophyll a was higher and Secchi disc visibility lower in inshore waters but there has been no deterioration in these areas since the 1980s. The conductivity remained unchanged, although it was about 50% greater in the semi‐enclosed Nyanza Gulf than in the open lake. The water quality of the lake has therefore improved considerably despite the fact than concentrations of plant nutrients have not decreased and the reasons why this may be the case are discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
