I've never heard this song, but I've seen the Green River in Kentucky and it seems to fit George's song, sandbars etc. But ships?It's the same Green River in "Paradise":
Daddy won't ya take me back to Muhlenburg County,
Along the Green River where Paradise lay.
I routinely cross over the Green River in Henderson County where it really is green instead of blue or gray. I always heard that it was so deep that the refracted light was green instead of blue. I don't think that really makes sense though.
The sandbars are in the headwaters which is a more remote part of Kentucky, away from population centers. Green County, Kentucky was featured in National Geographic several years ago. It's one of those places that you almost have to be going there to ever see it. It's just not on the way to somewhere else. ;-)