render your scene to a smaller texture like 512*512, then project that on a flat water plane. You make waves by offsetting the reflection map by a normal map like
tex2D(reflectsamp,texproject.xy+(normal.rg*0.01));
There are many other effects you can apply, like depth transparency, fresnel, etc.
If you don't understand what i'm talking about you might want to learn some of the basics first.
