Those of you who use Garmin GPS units may be interested in this map set of the Southeast USA. It has a lot more detail of the salt marsh and creeks than what I was using previously. Says it has "High resolution water data - lakes, rivers, streams, and washes”. It made my eTrex Legend 100x more usable and it is free. It is a large download.
http://www.gpsfiledepot.com/maps/view/101/
http://www.gpsfiledepot.com/maps/view/101/