Water hyacinth: A pain and gain for the African ecosystem

Water hyacinth is a fast-growing aquatic plant known for its beautiful flowers and significant ecological impact.

However, it is often considered one of the most invasive species in dams and rivers worldwide.

Water hyacinth can clog turbines, reduce water flow, and increase maintenance costs in hydroelectric plants such as the Rusumo Falls Hydroelectric Project, a joint initiative between Burundi, Rwanda, and Tanzania, generating 80 Megawatts of power for the three countries.

According to Patrick Lwesya, the project manager of Rusumo Power Company, water hyacinth is the main problem facing the power plant as it affects the amount of electricity supply.

“We get 10 to 15 tons of water hyacinth every day, and it clogs the intake part of the hydroelectric power plant, causing a drop of five megawatts in electricity supply. We often have to remove them manually,” says Lwesya.

Many large hydropower schemes across Africa are suffering from the effects of water hyacinth.

The Owen Falls hydropower scheme at Jinja on Lake Victoria is a victim of the weed’s rapid reproduction rates and an increasing amount of time and money is having to be invested in clearing the weed to prevent it from entering the turbine and causing damage and power interruptions.

Due to its potential to rapidly reproduce and spread, the weed has also inhibited activities such as fishing and transportation in the lake.

Lake Naivasha in Kenya is also severely impacted by the invasive water hyacinth, which disrupts ecosystems by depleting oxygen, blocking waterways, and promoting mosquito breeding.

This affects local livelihoods, particularly fishing, and reduces flood protection.

Water hyacinth is not only affecting East African countries. It is also 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.

According to experts, there are several popular control mechanisms for preventing the spread of or eradicating of water hyacinth.

The three main mechanisms used are biological, chemical and physical control. Each has its benefits and drawbacks.

“Chemical control is the least favoured due to the unknown long-term effects on the environment and the communities with which it comes into contact,” says environmental expert Dr. John Kakonge.

According to research done by Practical Action, the application of herbicides for controlling water hyacinth has been carried out for many years.

The common herbicides are 2,4-D, Diquat and Glysophate. It has been found that there is a good success rate when dealing with small infestations but less success with larger areas.

However, the main concern when using herbicides is the environmental and health-related effects, especially where people collect water for drinking and washing.

Dr. Kakonge adds that physical control, using mechanical mowers, dredgers, or manual extraction methods, is widely used but is costly and cannot effectively deal with very large infestations.

Patrick Lwesya says the water Hyacinth at the Rusumo power plant is becoming difficult to manage manually by the day due to the increase of the invasive plant in River Kagera.

“The manual control is becoming hectic for us, so we are planning to install floating blooms to prevent water hyacinth from coming to the intake because they are clogging the inlet and reducing the water flow," said Lwesya, who adds that they have already made a procurement plan for the floating booms from a company in Asia.

Floating booms are utilized to create a barrier to stop oil spills, debris, aquatic plants and algae, trash, and even marine life.

Biological control is the most widely favoured long-term control method, being relatively easy to use and arguably providing the only economic and sustainable control.

It involves the use of host-specific natural enemies to reduce the population density of a pest.

Dr. Kakonge says: “Several insects and fungi have been identified as control agents for water hyacinth. These include a variety of weevils, moths and fungi. Biological control of water hyacinth is said to be harmless to the environment as the control agents tend to be self-regulating.”

Mechanical or physical removal of water hyacinth is seen as the best short-term solution to the proliferation of the plant.

It is, however, costly, using either land-based ‘clamshell’ bucket cranes, draglines, or booms, or water-based machinery such as mowers, dredges, barges or specially designed aquatic weed harvesters.

Researchers and experts suggest that such methods are suitable only for relatively small areas.

Many of these techniques require the support of a fleet of water and land-based vehicles for transporting the large quantities of water hyacinth which is removed.

Mats of water hyacinth can be enormous and can have a density of up to 200 tonnes per acre.

Although water hyacinth is seen in many countries as a weed and is responsible for many of the problems, many individuals, groups and institutions have been able to turn the problem around and find useful applications for the plant.

The plant itself, although more than 95 per cent water, has a fibrous tissue and a high energy and protein content, and can be used for a variety of useful applications including as a source of animal feed, a component in biogas production, a fertilizer, and a raw material for various crafts and textiles.

It can also be used for wastewater treatment and as a substrate for composting.