Where can I find bathymetric data?
The USGS has made bathymetric surveys for many coastal areas and for a few selected rivers and lakes in the U.S., including Yellowstone Lake, Crater Lake, and Lake Tahoe. Information and data for some of those studies is on the USGS Maps of America's Submerged Lands website.
NOAA (National Oceanic and Atmospheric Administration) is the primary source of bathymetric data for the world's oceans. See their Bathymetry and Global Relief website.