Two shark sightings and several ocean incidents that left five people injured — four of them critically — kept lifeguards busy around Oahu on Sunday.

At about 8 a.m. two men were treated at Pier C at Kewalo Basin in Kakaako after a diving incident.

Shayne Enright, spokeswoman for the Honolulu Emergency Services Department, said a 35-year-old Washington state man was brought aboard his tour boat and given CPR after it was discovered he was not breathing underwater while scuba diving.

Honolulu EMS personnel took over with advanced lifesaving treatment and took the man in critical condition to a hospital, Enright said.

A 42-year-old man who dived in to rescue the first diver was treated by EMS for a quick descent into the ocean, Enright said. He was taken in serious condition to a hospital.

Other boaters at the harbor said Sunday that the injured men came from a boat operated by Ocean Legends, a tour company that has a boat called Maori Warrior at Pier C. The owner of Ocean Legends did not immediately return a call for comment. One man said Ocean Legends’ boat came speeding into the harbor Sunday morning, rocking other boats at the pier, and was met by emergency responders at the dock.

At about 11:40 a.m. a 66-year-old woman was found unresponsive in shallow water at Hanauma Bay, Enright said. Lifeguards started CPR before turning her over to EMS personnel, who treated her and took her in critical condition to a hospital.

Enright said the woman was using a traditional snorkel and mask.

At about 4 p.m. two swimmers were reported in distress off Sand Island in an area with no posted lifeguards. Responding lifeguards found a 57-year-old man unresponsive in the ocean and began CPR. He was taken in critical condition by EMS to a hospital.

The second man, 29, was treated by EMS at the scene but refused transport to a hospital. It was not clear how the men got into trouble.

Then at 4:30 p.m. lifeguards rescued a 39-year-old bodyboarder who became unresponsive at Makapuu. Lifeguards revived the man, and EMS personnel took him in critical condition to a hospital.

Lifeguards also responded to multiple shark sightings, Enright said. At about 4:50 p.m. lifeguards cleared the water at Makaha Beach Park and posted shark warning signs after a 7-foot shark was seen in the area acting aggressively. Then at about 5:20 p.m., lifeguards posted shark warning signs at Velzyland on the North Shore after a 6-foot shark washed up onshore and swam back into the ocean.

Enright said the busy day came as EMS prepared for National Emergency Medical Services Week, highlighting the importance of paramedics and emergency medical technicians. Enright said the city has 20 EMS stations, about 150 paramedics and 100 EMTs.