Canberra, Feb 15 (IANS): Dirty water from a flood crisis in north Australia has spread to parts of the Great Barrier Reef, placing it under stress, scientists have said.

The floods are the result of weeks of devastating rain in Queensland. Some regions experienced the equivalent of a year's rainfall in 10 days.

Aerial pictures show that run-off from one river has blanketed some reef areas more than 60 kilometres from shore, the BBC reported on Friday.

The UN calls the Great Barrier Reef, located in the Coral Sea off the coast of Queensland, the "most biodiverse" of all the World Heritage sites, and of "enormous scientific and intrinsic importance".

Scientists fear the sediment-laden waters may be blocking out light and effectively "smothering" coral.

In recent weeks, run-off from several rivers has coalesced to affect an approximately 600 kilometre stretch of the reef's outer edges, scientists said.

The water has not dispersed due to its size and a recent lack of wind.

Frederieke Kroon from the Australian Institute of Marine Science said the nutrient-rich water had also sparked algae growth in some areas, turning waters "a thick blanket of green".

The reef is already facing threats to its survival such as coral bleaching caused by warmer sea temperatures. It has also been damaged by cyclones.