It's hard to say exactly what is going on there, but the first thing I would check is that your boundaries are correctly configured. I would expect to see a difference in the shading between the water body and land area in your define map view, which I am not. Can you switch to the contour view and post a screen shot of what has been generated?
Double check that you do not have any map boundary duplicates, and that your main water body is configured as Shoreline, and then regenerate the map.