Take a good look at NOAA charts and check when the body of water was last surveyed. While lights, buoys and man made things are accurate, unless the body of water is used by Government or commercial shipping most US waters haven't been really surveyed in our boating lifetimes.

With the limited resources and large area to cover it makes sense to work the places of greatest need. I don't for see small rivers, creeks and bays getting an accurate picture of the bottom any time soon.

http://www.nauticalcharts.noaa.gov/hsd/NHSP.htm

http://www.nauticalcharts.noaa.gov/hsd/east_priorities.html