Cristiano Ronaldo might the newest Splash Bro ... 'cause he just Deep 6'd a reporter's microphone into a lake -- and it was all captured on video.
The soccer superstar was out in France when a reporter came up to him, put the mic in his face and asked if he was prepared for the big Portugal vs. Hungary match later in the day.
Ronaldo casually snatched the mic and lobbed it over his shoulder ... sending it to a watery grave.
The reporter spoke with BBC after the incident and said, "I'm not sure why he did it.