This is the world’s only semiaquatic viper, usually found in or near water, particularly in slow-moving and shallow lakes, streams, and marshes. The snake is a strong swimmer and even enters the sea. It has successfully colonized islands off both the Atlantic and Gulf coasts.
This snake must have been swimming in the water along the swamps bank. That is where the most duckweed is still growing. If we had not been above ground, on a small wooden bridge, this snake would have been invisible.