I work at a greenhouse and we use "SUNBELT" groundcover cloth that comes in 10',12',15' wide X 300' rolls. We used old pieces of material in 18-36" of water to create our spawning beds. Hopefully the material will keep the cattails from chokeing the beds. Covered them with 4-6" of common gravel and put some structure near by. There was constant activity there all season long. I hooked into a 3.5# SMB crusing the beds one evening on my 5-weight and a #12 nymph. WOW!!!! I haven't wet my pants since I was a kid.