Water hyacinth infestation in Lake Tana, Ethiopia: a review of population dynamics

Lake Tana, the largest lake in Ethiopia, has been severely threatened by water hyacinth infestation over the last decade, especially along the northeastern shore. Since this invasive weed is extremely difficult to eradicate, sustainable management strategies should be put in place to reduce negative impacts on local ecological and socio-economic systems; this requires a better understanding of the population dynamics. In this paper, we review the seasonal change of water hyacinth coverage in Lake Tana and explore its linkages with various environmental factors. During the rainy seasons, increased nutrient concentrations, humidity, and especially water level can promote the formation of extensive water hyacinth mats. In the dry season, diminishing lake water in surrounding floodplains, along with concomitantly increased temperature and solar radiation, may support seed germination and lead to the next life cycle. Currently, water hyacinth mainly occurs in northeastern Lake Tana due to coastal eutrophication, lake topography and westerlies. Expansion of the infested area is slowing down. However, further spread of water hyacinth is still possible in other parts of the lake basin due to changing climate and environmental conditions. Integrated control methods should be put in place in the near future to prevent water hyacinth infestation in Lake Tana, and upstream basin management is vital to reduce nutrients transportation into the lake as a long-term plan.