The research was carried out by the Australian Institute of Marine Science (AIMS), supported by the Marine and Tropical Sciences Research Facility and the Great Barrier Reef Marine Park Authority, using data collected since 1992.

The research has just been published in the authoritative scientific journal Ecological Applications.

The principal investigator, Dr Glenn De'ath, said seaweed cover showed the strongest response to poor water quality, increasing five-fold with declining water clarity. The diversity of corals was also affected, decreasing in poor water quality.

AIMS coral reef ecologist, Dr Katharina Fabricius, said: "Previously, research on the impacts of pollution on the Great Barrier Reef was conducted on local scales.

"For this study, we collected ecological data from 150 reefs and at over 2000 water-quality stations across the entire Great Barrier Reef Marine Park, making it a much broader study."

The Great Barrier Reef Marine Park extends 2000km along the north- east Australian coast, covers 345,000 square kilometres and is the largest world heritage area.

It contributes billions of dollars per year to the Australian economy.

"Our analyses have shown that on the Great Barrier Reef, critical water quality thresholds are 10 metres for Secchi disk depth (a measure of turbidity) and 0.45 microgram per litre of chlorophyll (a surrogate for nutrients). Beyond these levels of turbidity and chlorophyll, seaweed cover will rapidly increase and coral biodiversity will decline," Dr Fabricius said.

The findings from this study have already been used by the Great Barrier Reef Marine Park Authority to develop water quality guidelines.

"Currently, the water on 22 percent of reefs - about 647 reefs - on the Great Barrier Reef does not meet water quality guidelines," Dr De'ath said.

The study predicts that if water quality was improved in these areas, seaweed would be reduced by 39pc and the number of coral species would increase by 13pc. The paper can be viewed here.