Phase II (April 1998-August 1999): macrophytes covered 40% - 70% of the reservoir water surface. The large macrophyte patches triggered a serious problem with mosquitoes (Mansonia sp.), thus demanding its mechanical removal. This phase was characterized by the harvest of water hyacinth, low algal biomass, and the increase of water transparency and decrease of dissolved oxygen (DO).
Phase III (September 1999-December 2004) was characterized by the drastic reduction of the macrophyte cover on the water surface, along with an abrupt limnological changes such as a significant increase in chlorophylla, cyanobacterial biovolume, total phosphorus (TP) concentrations and pH values and a drastic decrease in water transparency and DO at the deepest layers of the reservoir. During this phase, the spring cyanobacteria bloom was replaced by permanent multi-specific cyanobacteria blooms, and the reservoir shifted to a hypertrophic state