Use heavy-duty PVC pipe to form concrete posts. The process is done by having two different diameters of pipe, one to fit inside the other. Make sure the length of pipe is long enough to go into the lake bottom by several feet. For ease of handling, it’s recommended that shorter pieces of pipe are used and coupled together as it goes deeper. Place the 12-inch diameter pipe on the floor of the lake bed and hold steady (this is where the eager volunteers come in handy). Use a sledgehammer to pound the 12-inch pipe deep down as far as possible. Clean out the muck from the pipe with post hole diggers.