Floating: It's like if flight and swimming had a lazy baby. It is an uncommon ability, usually seen from the Spectral armies of Therodos or other ghosts, making them slightly more mobile than other undead options.

Floating works underwater.

Specifically, floating allows:

• Crossing of river and mountain pass province boundaries at no movement penalty
• Immunity to Earth Attack, Earth Grip, other spells that specifically don't say "does not effect flying and floating units".
• Does floating grant immunity to tangle vines?