The Federal Maritime and Hydrographic Agency's website has maps and a great deal of information about leisure boating: http://www.bsh.de/en. Delius-Klasing publishers also have maps of coastal waters: www.delius-klasing.de.
Waterways
The "German waterways information system" - available on CD from the German Motoryachting Association - has lots of useful information about waterways in Germany: www.dmyv.de. A set of maps for the new Ruhr leisure boating area entitled "Leinen los - Spannendes Land in Sicht" (Cast off - fascinating land in sight) is available from Ruhr Tourist Information: www.sportbootrevier.de, www.ruhrgebiettouristik.de.
Inland waterway networks
Berlin Tourism Marketing's map of waterways in Berlin and Brandenburg has plenty of useful information and maps of waterways in Berlin/Brandenburg: www.berlin-tourist-information.de. A boating tour planner packed with information about the waters in Mecklenburg and the Brandenburg Marches is published by Quick Maritim Medien: www.quickmaritim.de.