The spread of an invasive alien species is neither easy to manage nor easy to reverse, threatening not only biodiversity but also economic development and human wellbeing. According to the United Nation Environmental Programme (UNEP), native to the Amazon Basin in South America, water hyacinth (water weed) has emerged as a dangerous weed in more than 50 countries in the tropical and subtropical regions of the world with profuse and permanent impacts.
Studies show that the weed was first introduced into Africa through Egypt sometimes between 1879 and 1882. It has been recognized as the most damaging aquatic weed in Ethiopia since its first presence in 1965. Its presence has been recognized in Lake Tana in 2011, according to Bahir-Dar Fisheries and Other Aquatic Life Research Centre, located at Bair-Dar University. Even though several efforts have been made by different parties, especially by communities, its expansion is increasing year after year.
According to the Research Centre, area coverage of water hyacinth has been increased at alarming rate. Its coverage at the inception period in 2011 was about 80 to 100 ha. After a year it has grown about 20,000 ha. Even if tremendous amount of human labour, time and money has been utilized each year mostly by surrounding communities and the university, its coverage only continued to escalate and reached 50,000 ha. in the subsequent years.
Ethiopia's largest; Lake Tana covers 832-square-mile body of water and is packed with ecological, cultural and historical charm. It is believed that the origin of Ethiopians and their civilization is from and around the Lake and its source, Nile, as it has been discussed in so many anthropological, historical and religious books. Located in the highlands of Ethiopia's second-largest State of Amhara the lake is currently at a great ecological risk.
The water weed has been spreading to the whole body of the lake due to little concern towards the risk. It is obvious that saving Lake Tana is highly on the hands of the government and research institutions than surrounding communities although they would play a crucial role in supporting the effort.
Due to the fact that, the lake has enormous water potential for hydro power and irrigation, the Ethiopian government is launching various development programmes to stimulate growth and reduce poverty with little concern toward water hyacinth as one of the top 10 ecologically dangerous and worst invasive weed. It is devastating towards the ecological life of the lake and most water researchers and environmentalists are warning that the lake may dry out if proper control mechanism is not utilized against the invasive water weed.
Studies show that if water hyacinth expansion continues towards the southern tip of Lake Tana, it will invade the Blue Nile River Starting from its source, and consequently the Great Ethiopian Renaissance Dam (GERD) reservoir.
According to Other Aquatic Life Research Centre and Fishers in Bahir-Dar city of Amhara State, the measure that has been taken to avoid or reduce the water hyacinth from and around the Lake did not succeed due to lack of knowledge about the biological formation of the plant. Eliminating water hyacinth from the Lake, requires complete clearance including individual plant fragments and tissues. However, the measures that have been taken by the Amhara Bureau of Environmental Protection and other concerned stakeholders seem to prove less effective.
Most of the farmers and some governmental bodies merely collect certain amount of water hyacinth with high cost and deposit weed somewhere, mostly around the shoreline. On the other day, because of the disturbance in the water the remnant of the plant will spread to most part of the area through wave and other issues, the Research Centre stressed.
In addition, site selection to deposit the harvested weed biomass is inappropriate. Drained input fertilizer and other agricultural influents from crop cultivated land and the catchment area of the lake aggravates water hyacinth to over dominate other floras. Therefore, according to Bahir-Dar Fisheries and Other Aquatic Life Research Centre, shore area floras which would be important fish breeding grounds and livestock forage source in the vicinity continue to get damaged.
Currently water hyacinth is greatly affecting fishing rates because mats of water hyacinth can block access to fishing grounds clogging and damaging eye of net and increasing costs (effort and materials) of fishing. Furthermore, the water weed tears gill nets and damage boat's motor which accrue to cost of fishing. It was indicated that this weed forms a dense impenetrable mats across water surface, limiting access from the reach of the people. Moreover, navigation and fishing have been obstructed, and hydropower, irrigation as well as drainage systems have been blocked.
Water hyacinth control methods that are often used include mechanical, chemical and biological control. However, water researchers advised that existing methods have often been insufficient to contain the aggressive propagation of the weed and viability of its seeds despite substantial monetary investments over the years, due to lack of continued support from the government.
Thus, Bahir-Dar Fishers and Other Aquatic Life Research Centre recommended that manual control method which is currently applied should be revised based on the biological nature of the plant. Besides, integrated approach such as manual, mechanical, chemical and biological methods through scientific procedures has to be implemented. There is also need for improvement of land use management in the catchment and along the rivers so as to reduce silt and nutrient loads.
In June 2015, the United Nation Educational, Scientific and Cultural Organization (UNESCO) has registered Lake Tana as a World Heritage site for its unique ecological biosphere reserve. It is an indispensible multi-purpose lake both nationally and internationally. UNESCO also recognizes the islands' rich historical, cultural and religious significance with deep ties to the Ethiopian Coptic Orthodox Church. However, the lake and people living on the shore and their relatively isolated location on islands are at risk in need of an integrated effort of the government as well as all stakeholders and developmental partners.