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< prev - next > Natural resources management KnO 100372_Water hyacinth control (Printable PDF)
Water hyacinth
Practical Action
The problem
Water hyacinth can cause a
variety of problems when its
rapid mat-like proliferation
covers areas of fresh water.
Some of the common problems
are listed below:
Hindrance to water
transport. Access to
harbours and docking
areas can be seriously
hindered by mats of
water hyacinth. Canals
and freshwater rivers
can become
impassable as
they clog up with densely
Figure 2: Water Hyacinth causes problems in
many regions. ©Paul Calvert/Practical Action
intertwined carpets of the weed.
It is also becoming a serious hazard to lake transport on Lake Victoria as large floating
islands of water hyacinth form, while many of the inland waterways of south east Asia
have been all but abandoned.
Clogging of intakes of irrigation, hydropower and water supply systems. Many large
hydropower schemes are suffering from the effects of water hyacinth. The Owen Falls
hydropower scheme at Jinja on Lake Victoria is a victim of the weeds rapid reproduction
rates and an increasing amount of time and money is having to be invested in clearing
the weed to prevent it entering the turbine and causing damage and power interruptions.
Water hyacinth is now a major problem in some of the world’s major dams - the Kariba
dam which straddles the Zambia-Zimbabwe border on the Zambezi River and feeds
Harare has pronounced infestations of the weed.
Blockage of canals and rivers causing flooding. Water hyacinth can grow so densely that
a human being can walk on it. When it takes hold in rivers and canals it can become so
dense that it forms a herbivorous barrage and can cause damaging and dangerous
Micro-habitat for a variety of disease vectors. The diseases associated with the presence
of aquatic weeds in tropical developing countries are among those that cause the major
public health problems: malaria, schistosomiasis and lymphatic filariasis. Some species
of mosquito larvae thrive on the environment created by the presence of aquatic weeds,
while the link between schistosomiasis (bilharzia) and aquatic weed presence is well
known. Although the statistical link is not well defined between the presence of aquatic
weeds and malaria and schistosomiasis, it can be shown that the brughian type of
filariasis (which is responsible for a minor share of lymphatic filariasis in South Asia) is
entirely linked to the presence of aquatic weeds (Bos, 1996).
Increased evapotranspiration. Various studies have been carried out to ascertain the
relationship between aquatic plants and the rate of evapotranspiration compared with
evaporation from an open-surfaced water body. Saelthun (1994) suggests that the rate of
water loss due to evapotranspiration can be as much as 1.8 times that of evaporation
from the same surface but free of plants. This has great implications where water is
already scarce. It is estimated that the flow of water in the Nile could be reduced by up
to one tenth due to increased losses in Lake Victoria from water hyacinth.
Problems related to fishing. Water hyacinth can present many problems for the
fisherman. Access to sites becomes difficult when weed infestation is present, loss of
fishing equipment often results when nets or lines become tangled in the root systems of