could please anybody tell me how it is called ? The swim pool in one of the episode of Californication had it. People were walking on it, it looked like there were going on the water surface. Then Hank Moody broke it and fell into the water.
You could but you need to build all sorts of hidden supports underneath.
In theory a thick polycarbonate (perspex/plexiglass/lexan) sheet could easily support the weight but you would have a job anchoring it so it couldn't tip over or tilt and flood. And there would be a big risk if somebody managed to slide under it and get trapped.