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In 2013, the invasive marine ctenophore Mnemiopsis leidyi was first recorded in a true lake, Birket Qarun in the Fayum, Egyptian Desert. In 2014, it expanded in numbers and was also recorded in lake El Rayan II, south of Birket Qarun. Both lakes are saline, with Birket Qarun currently more concentrated than seawater. In the hot summer of 2015, a huge mortality was recorded, with only few larvae surviving. Whereas previous invasions were made possible by transportation in ship ballast water, trucks transporting mullet fry from aquaculture facilities in the Nile Delta to Birket Qarun and Lake Rayan II triggered the Fayum invasion. This is the first ever record of a ctenophore in an inland environment. We do not expect this invasion to be permanent, but it may damage the lake fisheries in the years ahead.