The Foamy Seawater mat that Zhan mention from terra-man is non existent. As a matter of fact, the person's last upload to Renderosity was on Monday, November 22, 2004 at 8:54 am. Website and domain is off the "scope". But if you follow the tutorial, maybe you'll be able to create the foamy sea water that you want????

The "foamy seawater" material is located in my copy of Bryce 5 and 6.1 both.  It is preset located in B6.1 in "waters/turbulent/foamy seawater".