Why was WWII fighting in the south pacific dangerous?

Reason - The World War II in South Pacific was dangerous:

The duration of world war II is from September 1, 1939 - September 2, 1945. The South Pacific became the major theatre of war between the Axis and the Allies.

The underwater warfare was more dangerous as this included the highest casualty rate in world war II as compared to any American force. In addition to that out of 16,000 Americans who were on patrol, 3500 (which was of 22%) of them did return.

The war around this area was considered to be dangerous because there are chances that the battleships or the submarines could sink into the water leaving behind a greater number of deaths as compared to the war in the land areas.

Bloodiest battle:

Out of all, in the Pacific war, the battle in Okinawa was the bloodiest battle in which 100,000 plus Japanese died.