Specifically, passenger Shalina Hussain, was found unconscious in one of the Rose's heads.

Paramedics that were called in the area could not revive her.

In the meantime, the Australian Maritime Safety Authority and the New South Wales police are investigating whether sewage gas from the vessel's blackwater tanks may have been implicated in her death, and the raid sought to determine whether the rest of the fleet's tanks and gas meters were within compliance.

Moreover, Australia's Roads and Maritime Services department stated that all authorities are cooperating in order to conduct an environmental pollution and safety compliance campaign on commercial charter vessels at Blackwattle Bay Marina.

According to local sources, hazmat teams measured 'extremely hazardous' levels of hydrogen sulfide in the head where Hussain collapsed. Also, police authorities confirmed that there were unsafe levels of gas onboard.

Yet, the owners of the Lady Rose declined to comment on the potential causes of the casualty, citing the ongoing investigation.

Hydrogen sulfide is a foul-smelling gas produced during the decomposition of waste, and it is the compound responsible for the odor of rotten eggs. In small quantities it poses little harm; in highly concentrated doses, however, it is toxic and can lead to convulsions, breathing difficulties and coma within moments, according to OSHA.

Concluding, passengers allegedly complained of an overwhelming odor aboard the Lady Rose in the hours prior to Hussain's death, and according to the Herald, the crew of the Rose had voiced objections to the smell for months.