I recently discoverd that it is possible to share waypoints, routes and tracks between google earth and my humminbird chartplotter.
The attachment below is a track recorded on my chartplotter of the Santiam River this summer. You can actually go mess with the touring settings in Google earth and get it to give you a little tour of the river. I just thought it was kind of cool. While I don't really think you should try navigating a river by GPS, if you had these for all the rivers around at least you would know which side of the islands to go around.
Al