Ornamental plant ruins Lake Tana

Chris Simoens
03 September 2019
The water hyacinth already covers 54 square kilometres of Lake Tana in Ethiopia. How much are local residents willing to pay to contain the spread of this pest plant?

All over the world, local diversity is threatened by invasive exotic species, which multiply uninhibitedly outside their native range because they lack natural enemies. Ethiopia is no stranger to this phenomenon: floating fields of water hyacinth already covered 54 square kilometres of Lake Tana in 2018.

With its 3620 square kilometres, Lake Tana is the largest freshwater source of Ethiopia, and even of the Horn of Africa at large. It is the source of the Blue Nile, which contributes to 80 percent of the Nile water. The UN, through UNESCO, recognised the lake as a 'biosphere reserve'.

Numerous people depend on Lake Tana for their livelihood. Farmers get water for their crops and livestock from the lake, while fishermen can also be found there. In addition, Lake Tana offers opportunities for transport, tourism, mining, relaxation and religious practices. The problem? It is not easy to assign economic value to all these 'services'.

In addition to agriculture and fisheries, Lake Tana also offers opportunities for transport, tourism, mining, leisure and religious practices.

A papyrus boat on the shore of Lake Tana.
© Shutterstock

Ornamental plant from South-America

The presence of water hyacinth (or Eichhornia crassipes) was first observed in Lake Tana in 2011. The plant, native to the Amazon basin in South America, was, unfortunately, imported as an ornamental plant for garden ponds all over the world. Water hyacinth, which, under ideal conditions, doubles in just five days, turned into the world’s most invasive water pest plant, mainly affecting Australia, Asia, the US and Africa with disastrous consequences for the local economy and the environment.

With Belgian support, Ethiopian researchers examined how the unbridled growth of the water hyacinth can be contained. Lake Tana is a common good, which means that citizens can freely claim its services, but also that the responsibility for tackling the water hyacinth problem lies with the local community.


Under ideal conditions water hyacinth doubles in just five days.

1.5 months’ salary

The Ethiopian and Belgian researchers conducted a survey to find out to which extent neighbouring farmers are willing to pay to reduce the water hyacinth populations, both in terms of money and in terms of working days. 98 percent of respondents believe the water hyacinth is hampering them: the pest plant covers farmland, clogs irrigation channels and impedes lake access.

Overall, the farmers are willing to invest the equivalent of 1.5 months’ salary in order to get rid of the water hyacinth completely. Further research will examine the impact of the problem on other stakeholders such as fishermen and hydroelectric power plants. According to past research, investments have more than proven their worth: the benefits of water hyacinth control were found to be 124 times greater than its costs.

The researchers suggest that the government should carry out additional studies analyses in order to attach economic value to natural services, which should make it possible to take better-informed measures to protect these services.




This research was carried out within the framework of EVAMAB, a project financed by the Belgian Federal Science Policy Office (Belspo) to support the UNESCO biosphere reserves. Case studies were conducted in Benin, Ethiopia, Tanzania and Uganda. EVAMAB focuses on the economic valuation of ecosystem services (= services delivered by nature). CEBioS (see box) was also involved in this research project, together with the University of Antwerp, KU Leuven and the Université Libre de Bruxelles.



The research for this article was carried out with the support of CEBioS (= 'Capacities for Biodiversity and Sustainable Development'). This programme is financed by the Belgian Development Cooperation and is housed in the Royal Belgian Institute of Natural Sciences (RBINS). CEBioS supports a number of countries such as Benin, DR Congo, Burundi and Vietnam in the development of indicators to monitor their biodiversity. This should allow them to better report on their biodiversity within the UN Convention on Biodiversity.

Within CEBioS, ten people follow up on 'biodiversity and development', including support for research, information, awareness-raising, policy advice and publications on biodiversity and development in the South. CEBioS also organises short internship visits in Belgium and on-site workshops for institutions in developing countries. Besides, it makes the colonial archives of the former national parks accessible by digitising them.

Biodiversity Ethiopia
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