Tactical map editing - water

HI, I have the vanilla version of Medieval, and I wanted to make myself a map with an oasis in the desert. And in the middle of this oasis I wanted a small lake. The problem is, the waves of the sea make the lake huge for a moment just before it dissapears. SO, is there a way to disable the waves? I saw some maps in the game that had lakes with still water, so there must be some way to do it.
Thanks for any help.

And I would also want to know if it is possable to get palm tree forests onto a sandy desert or rocky desert map. In the editor, when I place textures with trees, the palm trees appear, but when I try the map in the game, the palmtrees arn't there...