The official reason more than a million fish have died in a river in Australia is the hot dry weather, which has caused drought in New South Wales among other areas.

Amid the arid conditions, large algal blooms have drawn the oxygen out of the water, killing all the fish in stretches of the Darling River.

Tides of dead fish are now lining the banks where they are rotting quickly in record breaking temperatures which have seen parts of New South Wales facing an entire week over 40C, and highs of 46C in the area where the fish died.

A clean-up operation is underway, but water experts have warned that more fish are likely to die as the heatwave conditions continue.

Critics of the local government argue the impacts of the drought have been significantly exacerbated by management decisions in the river basin, in which numerous dams, locks and weirs control the flow of water through the river. Irrigation systems also draw water from the river for agricultural use.

In response to the crisis, the New South Wales government has said it is planning to mechanically pump oxygen into lakes and rivers with solar-powered aerators.

Minister for regional water, Niall Blair, conceded the aerators are a quick-fix for a bigger problem.

“They are a Band-Aid solution – we admit that,” Mr Blair told reporters.

“Nothing will stop this fish kill unless we get proper river flows and water levels in our dams back up to normal. We are doing everything we can to try and limit the damage,” he said.

But it has emerged that the New South Wales government reduced funding for the river management system by 60 per cent in 2013. The basin-wide programme monitored the health of fish in the river and included a strategy for “sustained commitment” of 50 years with a goal of restoring fish-stocks to 60 per cent of what it was before the arrival of Europeans on the continent, according to The Guardian.

Since the cuts, the native fish strategy has been abandoned, maintenance has been delayed and audits of the environment have not been carried out.

This has meant local governments have had less information with which to make policy decisions regarding the health of the basin.

Murray cod at least 70 years old are among the native species which have died.

The New South Wales opposition government has said it will set up a special commission of enquiry – the equivalent of a royal commission in the UK – to examine what happened and how to prevent it occurring again in future.

Australian National University water expert Dr Daniel Connell said irrigation of crops had played a role in the deaths.

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“It’s a very predictable crisis,” Dr Connell said.

He said taking water from the system for irrigation had likely contributed to the poor water quality in rivers as well as the drought which is impacting most of New South Wales.

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