One Nation leader Pauline Hanson is copping flak for taking her senators to a healthy part of the Great Barrier Reef in an effort to disprove claims the icon is dying.

Ms Hanson donned a wetsuit and snorkel gear for her swim off Great Keppel Island on Friday, when she took aim at green groups for telling "untruths" about the reef's health.

Senators Malcolm Roberts, who has long argued the case for global warming doesn't stack up, and Brian Burston joined Ms Hanson on the trip to support tourism operators by showing the world the reef is alive and well.

But the trip has been criticised by conservationists, who say Ms Hanson had taken her senators and the media to a healthy section of reef unaffected by unprecedented coral bleaching caused by high water temperatures.