Take a look at the link below to see what specific mapping Garmin offers for each lake. For lakes classified as MaxDef, you won’t find a better map. These are lakes that Garmin has surveyed with their own boats within the last few years with absolute, top of the line sounders and equipment. In Texas, MaxDef lakes include Sam Rayburn, Toledo Bend, Fayette County, Austin, Falcon, Amistad, Palestine, Fork, Lewisville, Ray Roberts, and Texoma. For most of these lakes, most or all of the entire lake was mapped. For some like Toledo Bend (southern portion, 45 feet deep to shoreline) or Falcon (US only), MaxDef provides partial coverage.
Garmin also offers sourced data with 1-foot contours for another 100+ Texas lakes (labeled as HD). Garmin map search