Like they have said, you just almost can't see the structure itself. I sank some a few years ago with 1/2 inch PVC and I even capped the ends off to hold air so it would be easier to find. But that didn't help either. After the gps unit that I used when I sank them failed and I didn't save the waypoints I've struggled to find them again to mark them. But you can find the shadows with side imaging, still hard to see though.