It may be an invasive pest, known for choking waterways in many parts of the world, but water hyacinth is proving an unlikely source of fuel in flood-stricken South Sudan. The fast-growing aquatic weed is rich in biomass, organic material that produces energy, and is being harvested and turned into briquettes for use in heating and cooking. As a fuel, it's cheaper than wood-based charcoal and safer to collect than firewood.