I hate to take a guess since those photos lack adequate detail. Basically, it's tough to ID a wad of plant-mass since leaf-structure and staging is difficult or impossible to discern.
The best photos (for ID-purposes) will show close-ups of a single plant laid out in a palm or contrasting background with a common object include for scale-reference.
Off hand, I'm guessing it's one of the Potomogeton spp - but not sure which one. Maybe sago pondweed (Potamogeton pectinatus).

Kelly Duffie
Cypress, TX