Case study on river management: Lake Chad
It has fluctuated greatly during this period, shrinking by up to 80% in 1985, but reaching 19,000km² once more in 2001.
The River Chari - along with its tributary, the Logone - provides 90% of the inflow to the lake, while the remaining 10% comes from the Komadougou-Yobe River system. Three-quarters of the water entering the lake north of N'djamena originate from headwaters in the Central African Republic and, to a lesser extent, Cameroon.
The Lake Chad basin supports more than 20 million people. The local economy in the upper part of the catchment is based on fishing, agriculture and pastoralism.
However, people living around the lake lack access to safe drinking water and proper sanitation. More than 150,000 fishermen live on the lake's shores and its islands. The current estimate of annual fish production from the lake is 60,000 to 70,000 tonnes.
However, as a result of environmental changes since the 1970s, including fluctuations in lake level, there have been considerable changes in the fish fauna. These include high mortality, the disappearance of some open-water species, and the appearance of species adapted to swamp conditions in areas where they were previously unknown.
The raising of cattle, sheep and camels - by local as well as nomadic herders - is also economically important, together with cultivation of some traditional crops. The most common system is lake-bottom cropping or receding moisture cultivation, which has been a response to the contraction of Lake Chad.
Farming the lake floor
Villagers have shifted from relying entirely on fishing, to farming the emergent lake floor as flood water recedes. A few large-scale irrigation schemes (polders) developed on some parts of the lake shore have proven totally unsuited to the hydrological, climatic and cultural conditions in the Lake Chad region, and can be considered as complete failures.
Though still quite marginal, the production of spiruline (blue algae) seems to be gaining economic importance.
In addition to direct support for livelihoods, the lake also plays an important socio-economic role in regulating annual water supply, recharging groundwater, and helping to control flooding.