Dockbuilders.com has a couple of products that may fill your need. I haven't used either but noticed them when I was purcasing dock building kits last year.

http://www.dockbuilders.com/spa-n-deck-wood-finish.htm

http://www.dockbuilders.com/woodrx-deck-stain-sealer.htm

1 ac pond LMB, BG, RES, CC