This sample of my
Navionics map seems to be a bit more detailed for underwater topography.
I did a little investigating when I spotted that they named some of the under water mountains in the lake. The person I contacted at Navionics was sure that USGS was the one to name these features. This is the response that USGS sent back:
Underwater features generally are not shown on USGS topographic maps. I took a look at the USGS Geographic Names Information System (GNIS) database at U.S. Board on Geographic Names and found no features by those names listed in New Hampshire.
I am forwarding your inquiry to the GNIS Manager, for further response.
(I have not pursued the issue any further.)