Getting ready to build one in a few weeks on our place on the river. Been wanting to do it for a long time and we're finally getting around to it. The problem is We cant get a concrete truck down there. I've calculated that it would take about 700 #80 bags of quikcrete, so that's out. Have any of you ever built one for access to moving water? What did you do? I'm pretty sure we're gonna have to put something in the floor of it, or it'll get too muddy to use.