Analysis: Lake Tana: how an invasive weed is threatening its survival


Yihun D. (PhD) and Wondwossen T. (PhD), for Addis Standard

Addis Abeba, Oct. 23/2017 – Lake Tana is the largest lake in Ethiopia and the second largest in Africa. In recognition of the lake’s rich biodiversity and significant cultural heritage, UNESCO added the lake to its World Network of Biosphere Reserves in June 2015.

Lake Tana covers an area of 3,000 square kilometers, while its catchment area covers 15,000 square kilometers. Four major rivers feed into the lake, including Gilgel Abbay, which flows from the south, Gumera and Rib from the northeast and Megech from the north. Gilgel Abbay, widely regarded as the source of Abbay (Blue Nile), originates from the Ghion spring, which is considered holy. The Tana basin connects about two million people, the majority of whom subsist on agriculture, while the two largest cities in the Amhara region, Bahir Dar and Gondar, lie within the basin.

Lake Tana harbors dozens of medieval island monasteries. These monasteries represent important religious sanctuaries, centers of traditional learning, and core tourism destinations. The lake is also rich in bio-diversity. It is home to a large species of fish and birds, many of which are endemic to the lake. Moreover, the lake occupies an important place in the country’s plan for economic development. The water from the lake is utilized for hydropower generation and supports large-scale irrigation schemes in the lowland agricultural areas. The lake, thus, is at the nexus of a complex web of political, economic and socio-cultural interests.


A pristine view of one of the island monasteries of Lake Tana

Even though Lake Tana is central to the country’s aspiration for socio-economic transformation, its haphazard management by government authorities raises critical questions. A case in point is the Chara Chara wier and the Tana Beles hydropower project. While the Chara Chara wier was constructed around 1995, at the mouth of the lake, to regulate its volume for downstream hydropower generation; the Tana Beles hydropower project was completed in 2010, and relies on water diverted from the lake through underground tunnels. The diverted water, after hitting the power turbines, is discharged to the Beles River basin, which is used to irrigate state owned sugar plantations. It should be noted that the Beles River basin lies outside the Lake Tana basin system.

One shocking consequence of these projects has been the defilement of the majestic Tis Issat Falls (The Blue Nile Falls). Since the natural flow of the water is now tightly regulated at the Chara Chara wier, the Tis Issat Falls, located 30 kilo meters downstream, has lost its natural spectacle, and with it, it’s enormous tourism potential and iconic status as one of the enduring symbols of the country. Locals have suffered dire economic consequences as a result.

According to a report from the International Water Management Institute, the extraction of large volume of water from the lake has caused the water level to drop below the recommended level, thus precipitating extensive environmental and economic disruptions.

The drawdown of the lake led to the desiccation of reed beds and consequent loss of breeding habitat for fishes. It also made transportation on the lake difficult. Several boats have sustained damages, others have sunk, after hitting rocks exposed to the surface of the lake due to the receding waters. The extreme contraction of the lake has also damaged the papyrus beds that grow around the lake, which represent an important source of livelihood to the Negede people. Papyrus reeds are used to make marketable products such as tankua (canoes), baskets and mats. The drawdown diminished the wetlands around the lake, and encouraged recession rice farming, thus contributing to the growing pollution of the lake. These multifaceted crises reached their climax when a large swath of the lake’s shores was invaded by water hyacinth in 2011/2012.

Water hyacinth: What is it, and what are its effects?

Water hyacinth is an aggressive invasive weed that surfaces on water bodies, such as lakes, rivers, and dams. Research conducted on its productivity shows that it can reproduce itself every two to three weeks depending on the nutrient condition of the water body. The weed can grow up to a height of 1 meter. It has no known direct food value to wildlife, and hence is regarded as a pest. If left unchecked, water hyacinth can cover entire water bodies by forming thick floating mats.

Fully developed water hyacinth mats block waterways rendering water transportation and fishing difficult. Water hyacinth also adversely affects freshwater ecology. The mats limit circulation of air and water, thereby diminishing the level of oxygen in the water, which, in turn, threatens the survival of aquatic ecosystems such as fish. The mats also hinder the passage of sunlight beneath the water surface, thus obstructing the photosynthetic activities of underwater plant species and degrading the biological diversity of the lake. Reduction of biological diversity transpires a cascading effect on aquatic animals, which depend on plants for shelter and nesting. In particular, the fish stock, deprived of oxygen and food, could vanish from the lake, thus forcing the fishing industry––a permanent scene of the lake for millennia––to come to an abrupt end.

Because the weed is highly competitive, it easily interferes in the biodiversity of the wetlands beyond the lake, thus disrupting wetland agriculture and livestock rearing. The weed’s high water content means also that it expedites the evaporation of water from the lake’s wetland, thereby contributing to a further contraction of the lake’s areal extent.


A large swath of Lake Tana’s shore is invaded by water hyacinth

What efforts have been made to control water hyacinth?

According to local sources, water hyacinth was first observed on Lake Tana at Chera kebele of Dembya woreda around 2011/2012 (2004 E.C.). By 2015, a significant swath of the lake’s northern and northeastern shores could be seen covered by water hyacinth. Estimates suggest that the weed currently covers 25,000 hectares of the lake. Recent media reports suggest that the weed is spotted on the Abbay River as far as the edges of the Tis Issat Falls, demonstrating the weed’s capacity to expand itself to new areas.

Fragmented efforts to control water hyacinth have been going on since 2012. These efforts were mainly focused on mobilizing affected farming communities to uproot and dispose the weed manually. Needless to say, these efforts were utterly ineffective in terms of controlling the spread of water hyacinth.

The crisis, despite its catastrophic consequences, did not enter public consciousness until very recently. Credit must be given to the Amhara Mass Media Agency for bringing the issue to a wider audience. They have broadcasted a series of news reports, interviews, and documentaries about the invasion of the lake by water hyacinth. These programs have been crucial in informing the public about the scale of the problem.

As awareness grows, people soon start to talk about water hyacinth and Lake Tana. Environmental activists, civic society groups, singers, poets, writers, and ordinary citizens alike have all expressed their concern about the precarious condition of the lake. The issue has garnered substantial coverage both on mainstream and social media. This growing activism seemed to have registered with the government, especially at the regional level, as efforts to remove the weed have gained traction in recent weeks. A series of mass mobilizations was organized, some by government authorities, others by civic society and volunteer groups, to dispose the weed using manual labor.


A group of young men removing water hyacinth from Lake Tana

Besides these mass mobilization campaigns, three state universities located around the lake, namely Bahir Dar University, University of Gondar and Debre Tabor University, have been taking various initiatives to tackle the problem. Bahir Dar University is working in collaboration with a local engineering firm to build a customized mechanical harvester for removing the weed. Researchers at the university are breeding flies and studying the possibility of applying a biological control mechanism against the weed. The Geospatial center at the university is helping the effort by providing essential information about the growth and movement of the weed using reconnaissance survey and remote sensing techniques. University of Gondor, on its part, is building a mechanical harvester in house.

The regional government has recently formed a high-level steering and technical committee to follow up the issue. The Environment, Forest and Wildlife Protection and Development Authority of the Amhara Regional State seems to be the main body tasked with coordinating the ongoing mass mobilization of the public to remove water hyacinth using manual labor.

Conspicuously absent from the picture are the various federal level agencies working on water and environment related issues, such as Ministry of Environment, Forest and Climate Change, Ministry of Water, Irrigation and Electricity, and Minister of Agriculture and Natural Resource Development. Although these government institutions are, in one way or another, involved in the sustainable management and utilization of the country’s natural resources, their silence while the largest lake in the country is mired in a grave environmental crisis raises questions. Their inaction casts doubt on the commitment of the federal government to rescue the lake.

Generally, ongoing efforts to control water hyacinth are incommensurate with the scale of the problem. They are marked by poor mobilization of resources and lack of coordination and decisive leadership. The inaction of federal agencies, which are better placed to deal with the problem both financially and technically, has exacerbated the problem.

What can be done to control the weed permanently?

There are three established methods of dealing with water hyacinth: biological, chemical and mechanical. The biological control is based on introducing specialized insects to the weed infested area. The insects selectively consume water hyacinth and are believed to die subsequently. The chemical option involves applying herbicides that can kill the weed, whereas the mechanical option involves deploying specialized machines to chop, harvest and dispose the weed.

The chemical option is the least desirable as the chemicals used to kill the weed could pollute the freshwater of the lake and adversely affect its ecology. The chemicals could also enter humans via the food chain, and precipitate health problems.

Likewise, the biological option might produce unforeseen consequences. Because insects behave unpredictably, one cannot be certain that they will not compete with or even kill other native insects that serve as a source of food for fishes. In the worst-case scenario, the biological mechanism could pose direct health risks to humans and livestock. Moreover, it is a slow process, and might take decades before it could sufficiently remove water hyacinth from the lake.

Therefore, the least costly and the safest control mechanism seem to be the deployment of weed harvesting machines. This is a relatively straightforward approach, in which specialized mechanical harvesters are deployed on the lake to remove the weed and dispose it safely. Yet, the authorities have made little progress in this regard. The motive for not buying and deploying mechanical harvesters so far is not clear.

A simple Google search returns a large number of suppliers with price tags ranging from $30,000 to $100000. These machines cost far less than the V8 Toyota Land Cruisers that most senior government officials use for daily commute. The delay in deploying the machines is impeding the ability to control the weed at an early stage. Each day that passes without taking meaningful action against the weed is potentially fatal for Lake Tana. Although efforts by domestic engineering firms to create local capabilities for building harvesting machines is commendable, the idea of leaving the fate of the lake in the hands of these tentative experimentations seems naïve at best and irresponsible at worst.

How should Lake Tana be managed in the long run?  

We believe the invasion of Lake Tana by water hyacinth is the culmination of a plethora of environmental crises that have been afflicting the lake for years. Projects have been implemented on the lake haphazardly, without fully assessing their environmental and social consequences. When negative impacts transpire due to poor project planning or implementation, appropriate mitigation measures are rarely taken.

In recent years, the lake has come under increased strain from population growth, intensive agriculture, rapid urbanization and growing infrastructure development schemes. These challenges suggest the need to adapt a sustainable and integrated way of managing the lake’s resources.

Most critically, the government must consider the competing interests of the various stakeholders of the lake during project planning. Decisions should not be finalized at the top and forced down to local communities through political coercion. Instead, affected stakeholders should be given meaningful space to articulate their interests at the earliest stages of project planning. Government bodies have the responsibility to protect the interests of vulnerable groups, such as farmers, fishermen and inhabitants of the island monasteries whose livelihood depend on the survival of the lake.

Likewise, environmental conservation efforts need to be scaled up in the Tana Basin. Adequate resources must be allocated, and conservation works should be implemented in an integrated and sustainable fashion. There are established environmental conservation and water management practices from which the government can draw lessons, such as Best Management Practices (BMP).

The government continues to receive huge sums of money from donors for environmental and natural resource management projects. Part of this money should be earmarked to sustainably manage Lake Tana and its vast resource base. It is also worth considering establishing a separate government body, preferably at the regional level, that regulates, coordinates, and integrates conservation, infrastructural development, and investment activities around the lake. By managing the lake’s resources responsibly and sustainably, it could be possible to meet the pressing demands of economic development while also safeguarding the lake’s long-term survival. AS

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