Always nice to hear a good rendition of this song, so 'refresh'!

Having taken The Road to Jackson Town a few times, I can testify there is actually a geographic entity called The Lakes of Pontchartrain. If you look at the map the road passes between Pontchartrain and Lake Maurepas, which latter looks like a stranded arm of the larger lake. Here's some source info:

http://www.upress.state.ms.us/books/1695