The ability to read river features and know how to use them is a big part of what separates intermediate boaters from novice and especially beginners.  We often boat scout as we hop eddy to eddy down complex runs.  When we can't see our next destination, we get out and scout from shore - why take a chance on there being a nasty strainer below that blind drop.  Rivers are a very natural environment (most of the time) and have a great deal of variety.  This is what makes them challenging and a great deal of fun to paddle and explore.