Tiger Woods is teein' off on marine life -- and he's doin' it with a ripped bod.

Tiger shared a photo of him freediving in the Bahamas with his kids on Friday ... and from the looks of it, the golf G.O.A.T. bagged himself a pretty legendary lobster.

Seriously -- that thing is HUGE. Even Tiger looks amazed at the catch.

Not bad for a dude 1 month outta intensive rehab ... after getting booked for a DUI in May.

Keep enjoying that island sun, Tiger!