if you fish one lake exclusively, why not map it yourself, you probably already know it quite well anyway
1 colour icon for 5 ft depth
1 colour icon for 10 ft depth
1 colour icon for 20 ft depth
1 colur icon for 30 ft depth, and so one
and so on.....
mark the top of any shoals or rocks or interesting humps
viola you will then have the most accurate map of all