I've recently downloaded the Wings Over Vietnam Air and ground expansion pack gold, and unfortunately experienced the shimmering water effect.
I searched for solutions on this board, and found the Knowledge base solution which was to alter some Terrain Mesh and Height Offset numbers.
I tried various combinations of these, but nothing worked.
So I went into game Options and reduced Water Detail from High to Medium.
That fixed it.
WOV Gold is a wonderful package BTW. Love the trees, the new airfields, the rivers, and lots of men in straw hats to napalm.