If you go by The Swamp on the University of Louisiana campus it looks like a plush algae carpet.
It's not.
It is however being overrun by a hyperactive aquatic plant known as Salvinia minima Baker otherwise known as Water Spangles.
You can see the Water Spangles in the 1st picture below, taken at Cypress Swamp when the thickness of growth was about half what it is at the moment.