Environment Minister Vicky Darling has admitted water quality could have contributed to the poor health of fish in the Gladstone Harbour, in central Queensland, but investigation is ongoing, ABC News reports.

Darling has released the report based on tests conducted by the government and the Gladstone Ports Corporation over the past 10 months.

While the report shows no significant changes were observed in the water analysis, fishing and environmental groups have questioned the reliability of the data.

"Scientists from the department have actually verified the results from their collection and those from the Gladstone Ports Corporation," she said, emphasizing that the information is true and correct.

"The report that I have released today actually details the results based on all of those reports and has actually been verified."

Darling says the latest information should be enough for residents to stop worrying about dramatic changes in water quality.

However, she admits the water quality analysis does not explain the sick fish in the Gladstone Harbour.

"The issue of illness in fish is a separate issue which is being investigated by an independent scientific panel," she said.

"It may or may not have something to do with water quality and we need to wait for those test results."

Meanwhile, Queensland Health said it has interviewed a number of commercial and recreational fishers, and concluded that there are multiple causes to the reported skin problems of local fishermen, and this is not linked to the fish illness in the Gladstone Harbour.