 In addition to the biogas it produces, its by-product can be used as fertilizer.Other factors which may have contributed to the decline of the water hyacinth in Lake Victoria include varying weather patterns, such as El Niño during the last few months of 1997 and first six months of 1998 bringing with it higher levels of water in the lake and thus dislodging the plants.Heavy winds and rains along with their subsequent waves may have also damaged the plants during this same time frame.