I'm not a lawyer nor am I familiar with Virginia laws but here's some comments based on what I know about Mississippi law. As to whether artifacts in streams are salvage, the first thing to determine is whether VA law defines waterways as "waters of the state." Many states have made law changes over the years to clarify possession of waterways and in most cases these laws disallow private ownership of flowing streams and make the water channel (including any dry land that may be wet during an average wet season)public property. In this case, any artifacts in the waterway would be on public property and their removal would be subject to whatever archeological laws the state has. I would guess also that if artifacts were discovered that were not covered by archeological law, the discoverer would probably have to get a salvage permit in order to convert ownership from public to private. Depends on the law.

In Mississippi we have a number of WTBS-era vessels that were scuttled in navigable waterways to keep them out of Federal hands. One notable one in central Mississippi is the "Dot", a riverboat scuttled in the Big Black River. It is still visible during low water periods but no individual can make any attempts at recovery without state permission. The state has not seemed interested in approving anyone to attempt salvage (in this case I prefer "historical artifact preservation"). Two or three years ago when we had low-water conditions due to a drought, an individual publicly proposed a recovery effort. In that specific situation, he never got to the point of getting state permission because the Corps of Engineers refused him a permit to make changes to the river bank to allow heavy equipment access.