The pillars stretching the rest of the way across the river. Many of them are always in the water, only getting down to the river mud on extremely dry years, and that mud is a poor surface to put a rope on, much less your feet-usually up to your knees. Boat access is preferred, dry/cheap old ropes reccommended, and using care not to drop anything expensive in the water..well, obvious.
Most people access the pillars that are directly in the river by canoe or similar craft. The james river can be nasty to swim in, so a stick clip from the boat and/or a small rack of gear for an "anchor" anchor can allow you to not drift off while belaying.