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Sagittaria sp.
Aquatic plant seen growing in the swamp. Duck potato is also called katniss or arrowhead, among other common names.
Barataria Preserve of Jean Lafitte National Historical Park and Preserve.
Could be... I don't know Louisiana plants. There are something like 10 species of Sagittaria there. If you go down the Wikipedia link I added and see their ranges you will see. S. latifolia is the one that pops up when you google the genus and Louisiana, but there are several others you can look into.