Plumes of polluted water from devastating floods and record-breaking rainfall in north-eastern Australia have spread to parts of the Great Barrier Reef, adding further stress to the beleaguered natural wonder, scientists said Friday.

The freshwater flood plumes carrying debris, sediments, nutrients, and other pollutants into the coastal regions came from weeks of devastating rain around the city of Townsville.

Scientists shared aerial pictures showing run-off from one river blanketing some reef areas more than 60 kilometers from the coast to the outer reef.

Researchers from the Australian Institute of Marine Science (AIMS) measured the extent and quality of flood plume waters in areas of the Great Barrier Reef when the mainland rivers were flooding.

“We measured low salinity levels in surface waters along a 600 kilometer stretch of coast,” Frederieke Kroon, the water quality team leader for AIMS, told dpa in a statement.

“In some locations, such as Cleveland Bay off Townsville, surface salinity levels were 20-24 ppt (parts per thousand) or roughly half the normal level of ocean water, of around 35 ppt.”

“This indicates a large amount of freshwater entering the Great Barrier Reef.”

The Great Barrier Reef, off Australia’s north-eastern coast, is the world’s largest coral system – covering an area larger than Italy – and is one of most biodiverse ecosystems on the planet.

The reef is currently recovering from two back-to-back coral bleaching in 2016 and 2017, as well as damage from Tropical Cyclone Debbie in 2016, and an ongoing outbreak of Crown-of-Thorns starfish.

The researchers are also measuring water clarity, nutrients, chlorophyll, and sediment concentrations in the flood waters. The test results are yet to be made public.

High concentrations of pollutants will reduce light availability in reef waters, affecting the growth of coral and seagrass communities, Kroon said.

“Now we have seen extensive flood waters on the Great Barrier Reef and AIMS researchers are increasingly concerned about the ability of the reef to recover from such frequent and large-scale disturbances,” Kroon said.

The Great Barrier Reef is a top tourist attraction in Australia, generating some 6.4 billion dollars (4.7 billion US dollars) a year and providing more than 64,000 jobs.

Townsville and other parts of Queensland experienced massive floods following heavy rains in recent weeks, with some areas experiencing rainfall equivalent of a year’s worth in 10 days.

Crocodiles and snakes were spotted near homes in the suburbs, and two people were found dead in floodwaters in Townsville.