In Iowa we have two classes of rivers. Some larger ones bear the enigmatic name "meandering rivers" and these belong to the state so we are allowed to touch the river bottoms and use sandbars that appear as water levels drop. The vast majority are "non-meandering" and on these the river bottoms belong to the land owners that own the shore. We are still allowed to float these waters but access to the banks and river bottoms is restricted.
David