Paul Brady's website provides two and only two songs in tablature form, and "Lakes of Pontchartrain" in one of them. His arrangement is in open "D" tuning, capoed at the fourth fret, which if I'm not mistaken translates to the key of F# (or Gb is you prefer).

See the list of "Related Threads," above ~ two or three of them (which should be among the most-recent related threads at the top of the list) contain links to the Paul Brady website's tab, and there is plenty of discussion about South Louisiana geography, meaning of the word "Creole," and what Irishmen were doing on the south shore of Lake Pontchartran in the 1830s. I have already repeated myself on these subjects more than often enough on these topics, but nyone interested can find plenty of discussion on this site about this song.