Where to fish during a Blood Moon?

[Goblin King]

I want to fight the three unique monsters that can spawn from fishing during a Blood Moon, as well as the "Advanced Combat Techniques" book.

The wiki doesn't tell me where I should fish during the Blood Moon. Does it need to be done on the surface? Can I fish deep underground where I'm considerably safer? Can I fish the four monsters from the lava?

The four monsters:
- Hemogoblin Shark​
- Blood Eel​
- Dreadnautilus

[Rumpus]

I've found them all from fishing in just surface, but I believe they can be encountered anywhere.