Aswan Dam environmental problems, these have proved to be significantly less severe than was generally expected, or currently believed by many people." Another observer disagreed and he recommended that the dam should be torn down. Tearing it down would cost only a fraction of the funds required for "continually combating the dam's consequential damage" and 500,000 hectares of fertile land could be reclaimed from the layers of mud on the bed of the drained reservoir. Periodic floods and droughts have affected Egypt since ancient times. The dam mitigated the effects of floods, such as those in 1964, 1973, and 1988. Navigation along
Aswan Dam mere 460 tons in 1968, but then gradually recovered to 8,590 tons in 1992. A scientific article in the mid-1990s noted that "the mismatch between low primary productivity and relatively high levels of fish production in the region still presents a puzzle to scientists." A concern before the construction of the High Dam had been the potential drop in river-bed level downstream of the Dam as the result of erosion caused by the flow of sediment-free water. Estimates by various national and international experts put this drop at between 2 and 10 meters. However, the actual drop has been measured