Little reddish plants floating on fresh water. I think they could be a fern?
Small plant floating on still water, often turns red in winter
Azolla rubra, growing on damp mud in seasonal pond
Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling duckweed or some mosses.