Very nice results. It hardly looks like an HDR shot, which is a compliment. I love the exposure and not overdoing the colors/strength as most (myself often included) tend to do with HDR. Just a really great photo. :-)
I too use Photomatix 4, so I'll have to keep that in mind with water. I've been reluctant to shoot water, given the ghosting obstacles that need to be overcome. Looks like photomatix handled it like a champ.