The altered ecological regime has also caused the introduction of two extremely invasive exotic plants. They have grown so prolifically that they have clogged irrigation ditches and caused damage to canals and pumps. In addition, granivorous birds have flocked to the rice fields and consumed as much as 50 percent of the harvestable crop. The increased bird population is linked to the year-round fresh water, food supply, and the nesting and breeding grounds created by the invasive exotic plants. This situation is quite similar to the invasion by Canada Geese of numerous cities and towns from Maine to the Eastern Coast of Florida.
The problems with the rice paddies notwithstanding, another major predicament is increased salinity, caused by the inability of the soil to drain. During pre-dam times, the annual washing-off of the floodplain, and addition of new soil, did not allow for salinity buildup. Now the salt leaches into the soil where few crops can grow in it.Recent rice production has been estimated at four tons per hectare, one-third of the twelve tons per hectare per year projected for these lands.
Similarly, “it has been reliably shown that malnutrition often follows dam building instead of the expected bounty resulting from newly irrigated lands.” The principle reason is that engineers simply do not understand the ecological benefits of the natural flooding cycle and its constructive impacts on ecosystems. In many regions across the face of the globe indigenous or local peoples, over centuries, developed an intensive and varied flood-dependent agriculture, similar to the one along the Senegal River. Once dams are built and an irrigation-based agriculture follows, the centuries old reliable array of local foods is replaced by an irrigated monoculture. Sustainable and diversified agriculture developed by local peoples produces more per hectare than irrigated agriculture, and is less destructive of natural resources, if for no other reason than scale.
Few formal evaluations have been made of the worldwide impact of dams. A decade ago, such a review was conducted.Its findings are discussed below.
 See generally, Itzchak E. Kornfeld, Groundwater Conservation: Conundrums and Solutions for the New Millennium, 15 Tul. Envtl L. J.365, 370, text accompanying note 42 (2002) (“near Perth in Western Australia, the clearing of forests of eucalyptus trees has caused shallow layers of salt in the soils of the country’s wheat belt.”)
 Vick, The Senegal River Basin.
 Marq de Villiers, Water at 125.
 See generally, Janet Abramovitz, Imperiled Waters, Impoverished Future(1996).