Barnaby Joyce has been called "irresponsible" by one of Australia's most senior conservationists after the Deputy Prime Minister dismissed wetlands adjoining Adani's Abbot Point coal port as little more than a "duck-shooting pond".

The brawl over Adani's threats to the onshore environment and the Great Barrier Reef escalated as Liberal backbencher Sarah Henderson broke ranks to question a potential $1 billion government loan to develop rail infrastructure for the Indian conglomerate's proposed Carmichael mine in Queensland's Galilee Basin.

Australian Conservation Council president Geoff Cousins said Mr Joyce had "failed to check his facts" on the Caley Valley wetlands, a 5000-hectare bird habitat that environmentalists say was damaged by coal dust contamination from the Adani terminal during cyclone Debbie.

Mr Joyce this week played down the wetlands' ecological value, describing it as a "swamp" built for duck shooters.