I found some plants! I went to the Tigre river delta and took a boat trip up the canals. I need plant IDs! If you can peg the species I'd be very grateful!
Lilaeopsis (brasiliensis?). No picture yet!
Some type of Hydrocotyle.
And most excitingly I found a new type of aquatic moss! It looks a little like fissidens moss but it has a much nicer green color, and seems to grow more robustly. Its absolutely gorgeous.