TThe Duchess, who has modified her program to take into account her pregnancy, was absent from commitments most of the day, which requires a bumpy four-wheel drive through sandy roads.
The couple flew to Hervey Bay on Monday morning, before boarding separate boats for their different days off.
The Duke was to visit one of Fraser Island's lakes to meet with local elders and park rangers to learn about the natural beauty, biodiversity and cultural importance of the island.
You will also hear about the history of the island's logging trade, as well as its use as a training base for the Australian Special Unit Z during World War II.
Afterwards, he will travel by boat to Kingfisher Bay, where he will conclude the visit with a walk along the jetty.