Dear Dan, Thank you for your answer and my apologies for the late answer. The problematic blue area is a flat area, the white is the northernmost Gulf of Aqaba - Eilat that was taken out by setnull from the raster. I have downloaded and tried Arc Hydro Tools-->DEM Manipulation-->Fill SInks, Sink Prescreening, furthermore Flow Direction with sinks as well as fill. Did I miss something?
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