Anthony Joshua clearly ain't sweating about whether his superfight with Deontay Wilder will ever go down ... 'cause it's kinda hard to perspire waist-deep in the Atlantic!!!!
The unified heavyweight champ hit Miami Beach on Sunday ... showing there's not a care in his rock-hard body right now about a possible AJ-Wilder tilt.
Joshua bro'd down with some buds ... splashed around in the water ... and toweled off on the sand -- all while everyone still wonders if he'll ever scrap with The Bronze Bomber.
Reports say it'll get locked in for next April ... but nobody's agreed to anything -- with Wilder shelving the talks so he can focus on his big fight with Tyson Fury on Dec. 1.
One thing we DO know?? Joshua's already in fight shape ... clearly.