Lake Manzala is in grave danger of suffering pollution from the drainage of industries, agriculture and urban sewage that affects the physio-chemical and biological parameters in the lake. A geographical information system (GIS)-based method of lake trophic status assessment was undertaken to study the spatial distribution of eutrophic conditions of Lake Manzala. In the present study, tabular data supported by field checks have been analyzed by GIS functions and operations to assess, monitor and model the environmental conditions of the lake. A representation of the spatial distribution was developed using the inverse distance weighted (IDW) interpolation method. The eutrophic state index was calculated to describe the state of the lake's environment. A GIS overlay technique was applied to synthesize the information into a final map illustrating the spatial distribution of eutrophication conditions within the study area. The different levels associated with trophic status classification using GIS were then discussed in relation to environmental change and external loading from tributary inflows. The study revealed that the lake changed to eutrophic freshwater. This change is due to the increase of freshwater inputs and nutrient loading associated with agricultural land reclamation and urban waste disposal.