WordNet (r) 3.0 (2006):

white water
    n 1: frothy water as in rapids or waterfalls [syn: white
         water, whitewater]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "white water":
   breakers, collar, foam, froth, head, lather, meringue, mousse,
   offscum, puff, scud, scum, sea foam, soapsuds, souffle, spindrift,
   spoondrift, spray, spume, stinging, suds, surf