<P> Sediment deposited in the reservoir is lowering the water storage capacity of Lake Nasser . The reservoir storage capacity is 162 km, including 31 km dead storage at the bottom of the lake below 147 m above sea level, 90 km live storage, and 41 km of storage for high flood waters above 175m above sea level . The annual sediment load of the Nile is about 134 million tons . This means that the dead storage volume would be filled up after 300--500 years if the sediment accumulated at the same rate throughout the area of the lake . Obviously sediment accumulates much faster at the upper reaches of the lake, where sedimentation has already affected the live storage zone . </P> <P> Before the construction of the High Dam, the 50,000 km of irrigation and drainage canals in Egypt had to be dredged regularly to remove sediments . After construction of the dam, aquatic weeds grew much faster in the clearer water, helped by fertilizer residues . The total length of the infested waterways was about 27,000 km in the mid-1990s . Weeds have been gradually brought under control by manual, mechanical and biological methods . </P> <P> Mediterranean fishing and brackish water lake fishery declined after the dam was finished because nutrients that flowed down the Nile to the Mediterranean were trapped behind the dam . For example, the sardine catch off the Egyptian coast declined from 18,000 tons in 1962 to a 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 ." </P> <P> 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 at 0.3--0.7 meters, much less than expected . </P>

Building the aswan high dam had all of the following effects on agriculture in egypt except _ _