I just found this on the Nebraska Game and Parks Commission site. "Remember: Only the water belongs to the state of Nebraska. The stream beds and all adjacent lands are the property of the landowner through which the water flows. Appreciate the fact that you have the privilege of using the waterway. Nebraska statutes give you the right to portage around fences and other obstructions; however you are responsible for any damage you may do.  You must have the landowner's permission to picnic or camp."  So I guess a landowner could chase you off a sandbar in the middle of the Platte since it is his property allthough that seems very unlikely ???  Loading under a bridge should not be a problem since that should be within the R.O.W. of the highway?? Should be about the same for most states??