lance,
thinking "outside the box"
could you draw the outline of the waterbody in question
save in qgis or similar,,,,, by creating a color filled poygon
then export as shp file
then import to AC???
or alternatively maybe beter for you.....
do similar in google earth
save image...... satellite overlay or colored polygon (whichever u choose)to create as well save as kml
and use the image file as a background IMG with transparency within AC
probably a lot of work depends on what u need it for
hope that makes sense
DS