Marcio Freire -- a big wave surfer whose career was so iconic it was featured in the popular 2016 "Mad Dogs" documentary -- is dead after a tragic accident in the water in Portugal.
The Brazilian surfing veteran had been hitting the massive waves at Praia do Norte beach in Nazare on Thursday, practicing his tow-in ... when authorities say he fell off his board.
According to the Portuguese National Maritime Authority, rescuers found the 47-year-old in cardio-respiratory arrest ... and immediately started "resuscitation maneuvers on the sand.