Did you cut holes in your terrain with the cut tool?
On the terrain panel there's a little scissor icon you can click and use. If you click it and erase with it (right click) it will fill the holes back in if you cut them.
If it's not that the terrain is probably just too low or the waterplane object is too high.
A screenshot might help identify what's up.
Last edited by SniperHF; 17/09/17 06:46 AM.
