Coastguards and lifeboats from Seahouses recovered two people from the water near Beadnell Harbour after cries for help were reported to Humber Coastguard.
At 7.40pm a woman dialled 999 for Coastguard assistance after hearing a female shouting for help from the water.
Two shore divers went into the water to assist the woman and brought her safely ashore. The casualty informed her rescuers that her male companion had become ill and was still in the water. The man and woman had been snorkelling when the incident occurred.
Seahouses and Craster Coastguard rescue teams and Seahouses lifeboat and inshore lifeboat began a search of the area and quickly located the male casualty due to the bright yellow flippers which he was wearing.
Humber Coastguard scrambled a military helicopter which rushed him to Wansbeck Hospital. He was pronounced dead on arrival despite lifeboat and helicopter crews both performing CPR. The man has not yet been named.