SOME locals in the port town of Gladstone recall swimming and catching mud crabs off Curtis Island in the city's harbour. The harbour is now undergoing the biggest dredging operation ever approved in Australia. From 2014, huge ships are due to load liquefied natural gas (LNG) from Curtis Island for export, mainly to Asia. Mud crabs, fish and other seafood have erupted in lesions, red spots and other signs of sickness.

Gladstone harbour lies within the World Heritage Area of the Great Barrier Reef, an area the size of Italy stretching along the coast of Queensland. It was listed as a heritage site for its coral reefs, seagrass habitats and rare marine species, but worries about the impact of the harbour's rapid industrial development led to a recent visit by UNESCO experts. They are due to issue their report in late June.

The harbour at Gladstone already hosts an aluminium smelter and a coal-export terminal. But Australia's coal-seam gas boom inland is changing its face. Three consortia involving BG Group, a British company, and Santos and Origin Energy, both Australian, are each building on Curtis Island what will be the world's first plants to turn gas drilled from coal seams into LNG for export. A fourth plant is planned.

Seafood businesses commissioned Matt Landos, a veterinary scientist, to investigate outbreaks of sickness that have appeared among the harbour's abundant marine life. His report in April detailed how creatures he caught in the harbour suffered skin ulcers, diseased fins and damaged intestines. Mr Landos blamed toxic metals and sediment from earlier industrial pollution that had settled on the harbour bed and was being stirred up by dredging.

Leo Zussino, the head of the Gladstone Ports Corporation, a state body, rejects this analysis. He says “all the evidence” links the outbreaks to vast freshwater flows from floods and cyclones that lashed Queensland in early 2011; “generational change” to the harbour's salinity level followed. Mr Zussino blames sickness in the harbour's barramundi, a local fish, on stress from invasions by freshwater barramundi during the floods. “Science will win in the end,” he says.