The water hyacinth is a foreign weed introduced in the early 1990s to Nigeria. Since then it has spread rapidly to two-thirds of the country's rivers.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/invasive-foreign-plant-chokes-nigerias-rivers-and-dams
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/al-jazeera
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rivers
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/dams
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/invasive-alien-species
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/nigeria
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/africa