Rock which does not cover,
Coral reef, detached,
Wreck always partially submerged.
A number of sunken wrecks,
Obstruction of any kind,
Limiting danger line.
Foul ground, discolored water,
Yeah, stay away from those "Foul" zones! Those sea-umpires will just as soon write you out a ticket as look at you.
"Existence doubtful"? Now that's what I call Descartography.