Lake Tana in danger of water hyacinth

Water hyacinth in Lake Tana

Lake Tana is situated on the basaltic Plateau of the north-western highlands of Ethiopia covering an area of about 3,150 km2 with an elevation of 1830 m and an average depth of 8 m. The lake is bordered by low plains in the north (Dembea), east (Fogera) and south-west (Kunzila) that are often flooded in the rainy season. Lake Tana has multidisciplinary uses for example fishing, electric power generation, transportation, communal grazing land and drinking for humans other animals, and a site for different birds. Wetlands are located all around the lake which has high potential for biodiversity and the wellbeing of the lake. Lake Tana sub basin with diverse ecosystem (the Lake, the wetland and the rivers) support unique endemic fish species in the world. 20 of the 27 fish species of Lake Tana are endemics to the Lake Tana catchment. Of economically important fish species of the lake, there is one cichlid, Oreochromis niloticus (Nile tilapia), which is the most widespread species in Africa; The catfish family (Clariidae) is also presented by one species, Clarias gariepinus (African catfish) and The largest fish family in the lake is the cyprinids which are represented by four genera: Varicorhinus, Garra, Labeobarbus and Barbus. Despite this unique fish biodiversity and its high economic value, fish resources are under pressure from several threats. The major threat is illegal fishing, habitat destruction (wetland, rivers and the lake itself) due to human intervention; encroachment and pollution are the major ones. Now the above mentioned notorious weed called water hyacinth has been introduced in Lake Tana through unknown reasons and agents at a moment. The purpose of this preliminary survey was therefore; to investigate the incidence and estimate infested area coverage of Lake Tana.

Recommendations

The incidence and depth of water hyacinth infestation in lake Tana is still at its infant stage as a result can be controlled and overcome its problem easily. But when not controlled as soon as possible, water hyacinth will cover the lake, surrounding wetlands, tributary rivers and rice farms entirely; this dramatically impacts water flow, blocks sunlight from reaching native aquatic plants, and starves the water of oxygen, often killing fish (or other life in the water). The plants also create a prime habitat for mosquitoes, the classic vectors of disease, and a species of snail known to host a parasitic flatworm which causes schistosomiasis (snail fever). Hydroelectric power, transportation and irrigation schemes will be definitely victims by the invasive weed. Generally water hyacinth remains a major problem where effective control programs are not in place. As chemical and mechanical removal is often too expensive and ineffective, researchers have turned to biological control agents to deal with water hyacinth, but this has also a limited success and time taking properties there has to be exhausted studies on ecosystem interactions prior to the introduction of weevils.

Among the short-term control measures there are physical (mechanical and manual) removal and chemical control. All have serious constraints for implementation in water bodies of developing countries of the tropical and sub-tropical regions. Mechanical removal requires the purchase of harvesters, many of them too costly for most of developing countries. Even though Manual removal requires a large labor force, and Governments of the developing world do not always have the means to pay for this operation, this would seems the best means of controlling the weed in Lake Tana.

Water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. But it also produces large quantities of seeds, and these are viable up to thirty years. Therefore, long-term eradication measures have to be designed. Read the full article here