Two of three men who were involved in separate water-related deaths since the weekend have been identified, but only one is a confirmed drowning victim, the city medical examiner said yesterday.

Nathan C. Akee, 46, of Kane'ohe, died Sunday while free diving off Kualoa Regional Park. The cause of death has yet to be determined by the Medical Examiner's Office.

Mineo Tsunamoto, 63, of Japan, died Monday during an excursion to the sandbar in Kane'ohe Bay. The cause of death in that case also has yet to be determined by the medical examiner. Tsunamoto was brought to the He'eia Kea Boat Harbor after firefighters got a call at 4:06 p.m. for a near-drowning, said Capt. Kenison Tejada, a spokesman for the Honolulu Fire Department.

Tsunamoto died about an hour later at Castle Medical Center. No other details were available.

The third victim, a 44-year-old Kapahulu man who drowned while free diving off Waikiki, has not been identified, the medical examiner said. It is not clear if he drowned Saturday or Sunday, when his body was found.

In the first case, Akee and a friend were a mile off Kualoa on Sunday afternoon, Tejada said. The two were free diving from kayaks they had paddled to the area, Tejada said. At about 3:30 p.m., Akee's friend realized that he had not seen Akee for 20 minutes and began searching underwater, Tejada said.

"He found his friend," he said. "He had gotten snagged on something on the bottom. He freed him, got him up and secured him to the guy's own kayak. Then he went to shore to get help."

An off-duty police officer and an off-duty firefighter assisted by performing CPR on the way to shore but could not revive the free diver.

The unidentified Kapahulu man was found at 11 a.m. Sunday about 125 yards offshore from the Kapahulu Groin.

Firefighters were told on the beach that the man had gone diving Saturday, but city lifeguards, who pulled the man from the water, said that has not been confirmed.

Jim Howe, operations chief for the city's Water Safety Division, said lifeguards who had spotted a dive buoy offshore for most of the day were told by area surfers that a diver who had been there earlier in the day had gone home, Howe said.

On Sunday, a swimmer told lifeguards there was an apparent drowning victim offshore. Howe said the man was found face-down and wearing a weight belt on the bottom in 40 feet of water.

The victim apparently committed "the cardinal sin of diving" by diving alone, Howe said.

After four to six minutes without oxygen, a diver can suffer permanent brain damage or death, Howe said, noting, "If someone doesn't get to you in that time frame, it's over."

Although 40 feet is not deep by free-diving standards, Howe said the sport is physically demanding.

"It is a very, very strenuous physical activity," he said. "You are using large fins. You are going down to depth. You have gear. You are swimming long distances."

The medical examiner has not determined whether the Kapahulu man died of shallow water blackout, a condition that occurs when divers purposely hyperventilate in order to stay down longer. But Howe said the practice is common and dangerous.

There have been 20 confirmed accidental drownings through May, the medical examiner said.

Reach Mike Gordon at mgordon@honoluluadvertiser.com.