I have the following problem with Flow Direction Tool in my DEM and with such wrong calculated flow direction in the centre of DEM I am unable to delineate any watershed. What can I do?

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    Are you sure that is not a rendering problem? What are the pixel values in the dark area? – Aaron Apr 2 '15 at 17:54
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    Can you describe what we are looking at a little better and what you've already done to preprocess the DEM (Fill Sinks, Burn Streams)? My shot in the dark guess is we are looking at a water body and you may need to burn in stream lines to force flow direction to the water body's outflow point. – jbosq Apr 2 '15 at 17:59
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    You can always add a tiny slope to the flat surface before performing the analysis, using exactly the same procedure employed to remove slopes: see gis.stackexchange.com/questions/11440. – whuber Apr 2 '15 at 18:28
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    If that raster that you're showing is a flow-direction raster than to me it looks like it's been derived using the D-infinity algorithm rather than the D8. The watershed tool is expecting a D8 flow pointer grid as input. – WhiteboxDev Apr 2 '15 at 21:59