Water hyacinth (Eichhornia crassipes) — an aquatic plant native to South America — was once considered “the world’s worst aquatic weed” when it aggressively invaded Lake Victoria (Kenya), obstructing fishing channels and creating breeding grounds for disease-carrying mosquitoes. However, behind those decaying waxy green leaves lay a potential “gold mine” of renewable energy. By combining water hyacinth with livestock waste in biogas digesters, local residents have transformed an ecological disaster into a clean fuel source, offering a dual solution to Africa’s firewood crisis and indoor air pollution. The reading passage The problems and benefits created by the spread of the water hyacinth in Kenya (Cambridge IELTS 21 – Test 4, Passage 1) provides a practical perspective, balancing environmental challenges with community livelihoods.

Falling under the themes of Ecology, Renewable Energy & Sustainable Development, Reading Passage 1, which opens Test 4, features a clear line of argumentation, from the problem and technical mechanisms to social benefits. The test assesses candidates through three familiar question types: True/False/Not Given, Flow Chart Completion, and Note Completion. This article by ECE Language Center will help you fully decipher this test.

Reading Passage Content

The problems and benefits created by the spread of the water hyacinth in Kenya

[Paragraph 1] Water hyacinth (Eichhornia crassipes), an aquatic plant native to South America, first appeared in countries in Africa in the early 1900s. Scientists there called it the ‘world’s worst aquatic weed’, after it spread from the southernmost tip of Africa in the early 1900s and started obstructing major dams and rivers.

[Paragraph 2] In east Africa the plant arrived with Belgian colonists in Rwanda, who liked the look of its glossy leaves and delicate purple flowers floating in their ponds. But by the 1980s, it had ‘escaped’ out of the country via the Kagera river and made its way downstream to Lake Victoria. There, with no natural predators and perfect temperature conditions, the plant began spreading in the open water, blocking fishing routes and providing a new habitat for disease-carrying mosquitoes.

[Paragraph 3] For the women who smoke fish from the lake to sell it has meant declining income, as the boats that once brought the fish to shore by the hundreds struggle to navigate through the mass of plants. But water hyacinth isn’t their only headache. In order to smoke the fish that they buy, they must gather huge quantities of firewood, sometimes walking as far as 10km each way to collect enough to complete their work. And each day as they cook, they breathe in the thick, grey smoke. About three out of four families in Kenya depend on wood or charcoal to cook their daily meals, and the rate is even higher in rural areas, Kenya’s latest demographic and health survey shows. Using solid fuels like these for cooking increases indoor pollution. The World Health Organization estimates that about 14,300 Kenyans die annually as a result of indoor air pollution – most of which is caused by cooking and heating sources.

[Paragraph 4] Some years ago, on the shores of Lake Victoria, huge piles of water hyacinth that villagers had taken out of the water in an attempt to clear it were a common sight. But buried in those decaying waxy leaves was a renewable energy gold mine. It turns out the floating plant isn’t just good at spreading – its foliage also contains a high ratio of carbon to nitrogen. It’s a magic combination that has captivated researchers’ imaginations since as early as the 1980s when, across the world, they began to explore its potential as a biofuel. Just about 4kg of the dried plant would be enough to cater for a large family’s daily energy needs, early research predicted.

[Paragraph 5] In 2014, Nigerian academics announced they had got better yields of biofuel gas when they mixed the plant with chicken manure. A few years later, Kenyan scientists confirmed what their Nigerian peers and others had already found: manure worked to improve the process of converting the weed into gas.

[Paragraph 6] In 2018, the technology came to a village on the shore of Lake Victoria, called Dunga. The project promised a two-for-one solution to the dual menaces of the water hyacinth and dependence on firewood. The community received a pair of donated biogas digesters – machines that would transform a mix of water hyacinth and cow dung into biogas for cooking.

[Paragraph 7] The digesters work a bit like a stomach. The mixture goes in one end – think of it as a mouth – and over the next 20 to 30 days, it goes through a fermentation process and breaks down, giving off gas that comes out the other end. From there, the clean-burning gas is passed through pipes to the point of use, just like traditional domestic gas. In Dunga, the machines produce enough gas to serve about 60% of the village’s population. It is used in domestic stoves and for other household tasks such as purifying water and incubating chicks.

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