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This article needs to explain this phenomenon, which was a mystery to the ancients. It is caused by the rainy monsoons in the Ethiopian highlands, which receive heavy seasonal rains in the summer months; the runoff is carried by the Blue Nile down to Egypt, where the relatively flat delta prevents the water from quickly entering the Mediterranean & it floods its narrow lower floodplains. The Greeks were baffled by this phenomenon: not only by the fact a major river flowed thru the desert, but also that the Nile was practically the only north-flowing river they knew of, & they came up with all sorts of fanciful explanations for this nonseasonal flooding. They were also prevented from learning the actual cause for this annual flooding because they erroneously thought the excess water came from the White Nile, & exploration of its course was blocked by the Sudd, which proved impassable to both Greek & later Roman explorers. (All of this is common knowledge, & can be easily sourced -- some of it thru sources in either the main article on the Nile, or the articles I linked to.) -- llywrch (talk) 15:57, 14 October 2014 (UTC)