The last photographs Bethany Farrell uploaded to her Instagram account show idyllic scenes of the vivid blue waters of the Whitsunday Islands.

"It's a beautiful day down under," raved the 23-year-old British tourist, who had only just arrived in Australia on a gap year after finishing university in England.

"She should have been safe": Bethany Farrell. Credit:Instagram

A short time later, on February 17, the English literature graduate was on her first scuba-diving trip, at Blue Pearl Bay off Hayman Island in Queensland, when she was found lying unresponsive on the ocean floor.

Ms Farrell had become separated from her diving instructor during the course of the dive, her family claims. She was unable to be revived, and died at the scene.