Problems with the graphics rendering water

[Mazza]

I have a mac with a reasonably good if hardly top of the line graphics card (Radeon X1900) and the problem I have is that whilst small bodies of water such as swimming pools and small ponds are excellently rendered, complete with reflections, water detail and so on, the larger bodies of water cause the graphics to glitch and show the sea and larger lakes as red, green or black. This tends to settle if the screen is held still for a while but will resume if zoom in or out is used.

Is this an inevitable consequence of a crappy graphics card? Or is there anything to be done?