Saw an ad for used
Billboard Vinyl that got me thinking one of these might block the sun much like pond dye.
Not sure if I would attempt to float it with PVC pipes or some other scheme or just say fuggedaboutit and go with pond dye.
What are your goals? Dyes like Aquashade block blue/yellow sunlight, and can help block deeper aquatic plants, but do little to control shoreline plants and algae. Dyes applied at the manufacturer's recommended rate, can also disrupt the bottom of the food chain, which you don't want.
"IF" I was going to try to block sunlight in my pond, I'd start out by trying something affordable and manageable like pink insulation board, and get comfortable with the logistics needed. 8 sheets could cover a 16'X16' area for less than $100, so if it doesn't work, you haven't broke the bank. If it does work like you want, then you could always get more water resistant rigid panels if needed. Billboard vinyl would be great, but I would think it needs some type of grid flotation to keep it from sagging, and I wouldn't know how to do that in a manageable manner.