Ahhh…
A Trffid Queen (F) is creating new trees (7), (1) and shrubs (#), and to do so the game os painting fresh dirt (.) over the water, effectively replacing the water.
Because the queen creates land in front of it it can a floating or boating survivor who can, with patience, kite it into the water and create a strip of land. The only other way I know of to make new land out of water in the base game is to use the debug menu.