Water hyacinth

It sounds lovely and the flowers look lovely, but it can be a pest, as many people in tropical and sub-tropical areas will know. It can grow extremely rapidly to form mats which may be as much as two metres thick.

It has caused a problem in 2005 on Lake Victoria in both Kenya and Uganda. It was controlled using mechanical and biological means, with a 90% success. Given that it spreads quickly and also floats around, it's not surprising that it once again is causing a problem.
The problems it causes are:

• Hindering water transport
• Clogging various water supply systems
• Harbouring various diseases
• Causing water to evaporate nearly twice as quickly through transpiration
• Impeding fishing
• Unbalancing the ecosystem and reducing biodiversity.

Possible solutions:

• Biological control using a variety of insects and fungi. This method can take a long time to have an effect.
• Chemical control but this may harm the environment.
• Physical control by removing the weed - only suitable for small areas

Another approach altogether is to find a use for the plant. Possibilities, some realised, some still being investigated:

• Paper - the fibre needs to be blended with waste paper or jute to produce a reasonable quality (Bangladesh, Philippines, Indonesia, and India)
• Fibreboard - for general purposes indoors, and a bituminised version for roofing is being investigated (Bangladesh)
• Yarn and rope (Bangladesh)
• Basket work (Philippines)
• Charcoal briquetting - under investigation (Kenya)
• Biogas production - under investigation (Bangladesh)
• Water purification
• Animal fodder (China, Malaysia, Indonesia, Philippines, Thailand)
• Fertiliser (Sri Lanka)
• Fish feed - Chinese carp, tilapia, silver carp, and silver dollar fish will all eat water hyacinth.

If a commercial use can be found for the weed, then perhaps it can be kept under control on Lake Victoria. With so many potential uses, surely it's just a matter of time.
Sources: IRIN and PracticalAction

A very recent (January 2016) TED talk by Achenyo Idachaba covers some of the issues and offers one solution.  Achenyo Idachaba is the founder of MitiMeth, a social enterprise which aims to transform the ecological problem into enployment and products in Nigeria.