A cluster of crude stone dwellings stained with algae loomed suddenly out of the gloom on all sides. Here and there at the dark windows, Harry saw faces… faces that bore no resemblance at all to the painting of the mermaid in the prefects’ bathroom…
The merpeople had grayish skin and long, wild, dark green hair. Their eyes were yellow, as were their broken teeth, and they wore thick ropes of pebbles around their necks. They leered at Harry as he swam past; one or two of them emerged from their caves to watch him better, their powerful, silver fish tails beating the water, spears clutched in their hands.
-J.K. Rowling, Harry Potter and the Goblet of Fire