More than a fifth of Africa's freshwater species are threatened with extinction, and their disappearance could threaten livelihoods across the continent, according to a new study by the International Union for Conservation of Nature (IUCN).

The study, conducted for the IUCN's Red List of Threatened Species, assessed 5,167 African freshwater species over a five-year period. Two hundred scientists contributed to the report, which covers fish, mollusks, crabs, aquatic plants and aquatic insects such as dragonflies and damselflies.

As an example of how these disappearing species could impact the region, the IUCN points to Lake Victoria, the world's second-largest freshwater lake, where declining water quality and an introduced species (the Nile perch, Lates niloticus) have caused a reduction in the lake's native species over the last 30 years and as a result threatened traditional fisheries that any in the region depend upon for their livelihoods and food supplies. According to the study, 45 percent of the 191 fish species in Lake Victoria are threatened or even thought to already be extinct. Lake Victoria is located between Kenya, Uganda and Tanzania.

Sometimes overfishing is the problem, thanks to Africa's growing population. In Lake Malawi (located between Malawi, Mozambique and Tanzania), the population of one important fish species, Oreochromis karongae, has declined 70 percent in just the past 10 years. The IUCN has listed the species as endangered since 2004.

The fish aren't the only species in trouble. In the lower regions of the Congo River, 11 species of mollusk are threatened by pollution. Ironically, mollusks help keep freshwater ecosystems healthy by filtering out normal impurities.

"Africa is home to an astonishingly diverse range of freshwater species, many of which are found nowhere else on Earth," said the assessment project's leader, William Darwall, in a prepared statement. "If we don't stem the loss of these species, not only will the richness of Africa's biodiversity be reduced forever, but millions of people will lose a key source of income, food and materials."

The IUCN says it will use this study to identify priority areas and influence governments and developers to protect Africa's freshwater infrastructure.

Photo: Oreochromis karongae © Pr. George F. Turner, courtesy of IUCN.