SYDNEY, Jan. 8 (Xinhua) -- Around one million fish in Australia's Darling River have died, according to the New South Wales (NSW) Department of Primary Industries (DPI) on Tuesday, with important native species like bony bream, Murray cod and perch among the most affected.

The devastating environmental event, which occurred in a 40 km passage of the river near the township of Broken Hill approximately 1,150 km northwest of Sydney, was caused by toxic blue green algae and is the second such event taking place in less than one month.

With a large amount of algae in the river system, rapid changes in weather conditions can cause the aquatic plant to die.

When this happens and the organic material decomposes, a vast amount of oxygen is drawn from the water causing fish in the vicinity to suffocate.

"I've never seen two fish kills of this scale so close together in terms of time, especially in the same stretch of river," DPI Fisheries Manager Iain Ellis told the Australian Broadcasting Corporation.

"In both cases it's when the algal bloom has been disrupted."

"The first time due to a storm, and in this case, by the cold front that went through."

While some in the area have urged the state government to do more in order to prevent the alarming trend, a spokesman for the NSW Department of Environment and Energy said it's not an issue that water management could have solved.

"A fish kill of this nature is always very distressing but the causes are directly related to the current drought and cease-to-flow conditions," he said.

Currently, over 99 percent of NSW is suffering from one of the worst droughts on record.