Do a search for "floating islands" (search button at top in tool bar). There are some good threads here on doing what you are contemplating.

Get the water/dirt tested. I suspect you need lots of lime to off set the duck waste , lower the acidity of the area (pine country), and help clear things up.

Check these out ( and the included links):

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=102352&fpart=1

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=36712&fpart=1