Schoesser is correct, probably the water material parameter you want most to change is the "Becomes reflective at angle..:" on the 'Reflection' tab. On the 'Transparency' tab there is often a slider (maybe depending on which water material you choose) for "Murky Vs Clear".

People have created functions for changing the water to white at beaches or rocks, by creating a function driven by the distance to the ground under the water. Look for tutorials on "shoreline", "seashore", "function editor", etc.

Monsoon (mod of Vue forum at 3D Commune) sells a nice kit called SeaVue with lots of materials for white water, breakers on sand, white-capped waves, etc. He has several tutorials and cool freebies as well. I love his 'Ecowear' foreground ecosystems for land as well.

Check out my directory of Vue tutorials all over the web (please add suggestions when you find new ones). 

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'Art Head Start.com Free chapter, Vue tutorials, models, Web Tutorials Directory.