Odell Beckham Jr. -- I Believe I Can Fly ... On Water!!

Odell Beckham Jr. already dominates on football fields, soccer pitches, and basketball courts -- and now he's making the ocean his bitch, too ... by mounting a flyboard down in Miami.

The NY Giants star tackled the extreme water sport on Tuesday -- and as you'd probably expect -- he's already a pro. Paul Stoeppelwerth from Indy Flight Academy tells us ... OBJ got up and running on the flyboard on his first try.

If you haven't seen one of these things ... they're freakin' awesome -- kinda like a wakeboard that uses hydro-powered jets to hover up to 50 feet above the water! We're told most people take several minutes just to get upright ... but, of course, most people aren't Odell.

Stoeppelwerth says OBJ's "lower body is like a trunk, all the muscle memory from his football regimen definitely helps."