Vinnie,
I had a look at the site, here it is: http://www.dcr.state.va.us/parks/jamesriv.htm

I gave them a call, they seemed to think that flying an R/C seaplane would be OK, although I wasn't totally confident that they knew exactly what I was on about. The park is out of Richmond about 80 miles away, and I think I'd need to take a look before just turning up with a plane.

The Hanover RC web site has a set of photos of a float fly, but they've been there for at least a year with no indication of where the event took place. I'm going to their swap meet next weekend, so I'll ask about it.