FSX Sbuilderx Water Polygon Problem

Good day guys! I have a problem about water terrain in fsx. I've set the altitude of the water polygon to be '0' but as you can see at the picture, there is slope on the water.The land altitude is about 1 meter...How to fix this? Any ideas? Please?
The only time I have run into this problem is when I have had an ocean polygon meet a river polygon. The solution was to adjust the river polygon points down to 0 where it meets the ocean polygon, if the slope was small. If the slope was larger I would split the river polygon and create a sloped polygon running from 0 up to the elevation of the split.
Yup thanks Mike!...I've managed to find the culprit...the 'main island' somehow need to be at altitude of '0' for the weird slope to vanish...wonder why?
The only time I have had an island create a slope problem (when it wasn't caused by an adjacent river slope) is when the island was in a lake. The problem was caused by having Global Mapper "Get 'Elevations' From Attribute Value" using MODE_ELEV_M, the solution was to manually reapply the elevation of the lake in SBuilderX.