Water hyacinth is an aquatic plant which can live and reproduce floating freely on the surface of fresh waters or can be anchored in mud. Plant size ranges from a few inches to a metre in height. Its rate of proliferation under certain circumstances is extremely rapid and it can spread to cause infestations over large areas of water causing a variety of problems.
It belongs to the family of Pontedericeae, closely related to the Liliaceae (lily family). The mature plant consists of long, pendant roots, rhizomes, stolons, leaves, inflorescences and fruit clusters.
It grows in mats up to 2 metres thick which can reduce light and oxygen, change water chemistry, affect flora and fauna and cause significant increase in water loss due to evaporation and transpiration.
It also causes practical problems for marine transportation, fishing and at intakes for hydro power and irrigation schemes. It is now considered a serious threat to biodiversity.
It brings about hindrance in water transport; access to harbors 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 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.
It harbours a variety of disease vectors and therefore, a threat to human living directly. The diseases associated with the presence of aquatic weeds in tropical developing countries are among those that pose major public health problems such as 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.
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 the weed and the result of these problems is more often than not a reduction in catch and subsequent loss of livelihood.
In areas where fishermen make a living from their trade, this can present serious socio-economic problems. For example fishermen on lake Victoria have complained of much water hyacinth infestation.
They also complain that crocodiles and snakes have become more prevalent.
Problems with 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.
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 flooding.
Reduction of bio-diversity ;where water hyacinth is prolific, other aquatic plants have dfficulty in surviving. This causes an imbalance in the aquatic micro-ecosystem and often means that a range of fauna that relies on a diversity of plant life for its existence, will become extinct.
Diversity of fish stocks is often effected with some benefiting and others suffering from the proliferation of water hyacinth. People often complain of localised water quality deterioration. This is of considerable concern where people come to collect water and to wash.
Quantification of the problem is often extremely difficult. The real effect on fish stocks and flora is unknown. It is hard to calculate the effect on fishing communities.
Even quantifying the coverage of the weed is difficult on bodies of water which are as large and geographically complex as Lake Victoria. Satellite methods are the only accurate way of determining the spread of the weed.
Success is hard to measure when the exact scale of the problem is not clearly defined and is anyway growing rapidly.