by Stevanna E
This tessellation shows translational (slide) symmetry.
The "tile" (tile = repeating shape) is very neatly, precisely reproduced and fits with all the other tiles perfectly, without gaps or overlaps. That's what a proper tessellation does.
However, there's water with bubbles and coral. Water can be any shape. It's filler... stuff like air, filling the gaps. That's why this tile shape creates a valid abstract tessellation, but when we fill it with water, it is not an Escher-style tessellation.