Thanks for the info on Aquarians! It's definitely on my list now.
The triangle between Elysian Fields and Esplanade is the Marigny Triangle. The area between Elysian Fields and Press Street (railroad tracks) is also part of Faubourg Marigny. Bywater runs from Press Street (railroad tracks) to Poland Avenue. If you drive down Dauphine, or Saint Claude towards the Industrial Canal (or any of those streets that run in that direction, I think), you'll see a big sign at Press Street that says "Welcome to Bywater."
The link below contains the Historic District Landmark Commission's information regarding neighborhood boundaries.