You could, but then it would be fixed in place, forever.
Instead, I'd recommend getting some felt of the desired color, and/or painting it, and then cutting to size/shape desired (can reverse that order, if you prefer), and laying it on top of your other mat. That way, you have the flexibility to make it as wide/narrow as desired, can change shapes, and can move it anywhere needed, endlessly.
Seems to me to be a far better solution.
Thin, slightly textured acrylic pieces can also be used and cut to size and shape, if you want a more realistic, and shiny water feature.