JOIN THE CONVERSATION: Have authorities done enough to secure water supplies? Vote in our poll and have your say in the form below

WATER will be switched off to hundreds of farmers and town residents in the Mallee this week as the Murray River blue-green algae emergency worsens.

The toxic outbreak now involves almost 500km of the Murray River and has claimed reservoirs, rivers, wetlands and parts of Victoria’s two biggest irrigation districts. Taps were turned off to towns and farms in parts of the southern Mallee late Friday when the algal bloom reached key Wimmera Mallee pipeline pumps near Swan Hill, catching most residents unaware.

Experts said a record autumn heatwave, with temperatures soaring above 40C in northwest Victoria this week, was expected to grow the algal bloom until it choked almost all of the Murray River along the NSW-­Victoria border within weeks.

The Victorian Government has established an emergency response centre at Benalla with a second centre planned for the Mallee to help respond to the growing water crisis.

Deputy incident controller Bruce Wehner said it was likely the bloom would last weeks, even months.

“What we need now is heavy rain, cooler weather at least, a frost,” Mr Wehner said.

The Bureau of Meteorology has forecast a chance of thunderstorms in northern areas of the state this week but little chance of heavy falls. More than 50,000 megalitres of environmental water is being released from Lake Eildon over the next two weeks but there is little hope it will solve the problem. Inflows to river storages last month totalled 93 gigalitres, which is half the long-term average and in the lowest 20 per cent of records.

A spokesman for the Murr­a­­y-D­arlin­­g­ Basin Authority said the agency was “aiming to keep river flows as high as practicable in the coming weeks”.

“However, with falling storages and states advising of the likelihood of low opening water allocations for 2016-17, we also need to operate as efficiently as possible to maximise the volume of water held in Hume and Dartmouth Dams at the end of the season,” the spokesman said.

On Friday, water was turned off to farmers and residents in the Mallee towns of Culgoa, Berriwillock and Nullawil. On Monday at 6pm, Stage 4 water restrictions were imposed in the three towns along wtih Chinkapook, Chillingollah, Lalbert, Manangatang, Sea Lake, Ultima and Waitchie . The restrictions will stay in place until the crisis has passed. These seven Mallee towns will see their water switched off within days as the bloom passes Swan Hill and envelopes pipeline pumps at Piangil and Nyah.

A Grampians Wimmera Mallee Water spokesman said the towns still had water, thanks to their storages and the reverse pumping, but had lost access to Murray River flows.

Stage 4 water restrictions prohibit the use of water outside of the house with the exception that gardens may be watered by bucket or watering can filled directly from a tap. The restrictions will affect 780 households and 200 businesses.

Watering points have been established in the Mallee towns with orders starting to build for Grampians Wimmera Mallee Water emergency tanker visits but the 450 farms involved have been told they have to deal with stock water shortages on their own.

Many Mallee farmers have tapped directly into the pressurised pipeline to fill stock troughs without the use of feeder tanks.

GWMW is attempting to pump backwards through the pipeline from bigger storages at Culgoa and Berriwillock this week to give rural customers at least enough water to refill house tanks and troughs.

Residents fear the lack of water could be disastrous if any fires ignite.

The algal emergency occurred as Premier Daniel Andrews announced Wonthaggi’s controversial desalination plant would be turned on because of declining water storage levels across Melbourne, Geelong and Ballarat.

The desalinisation plant will deliver 50 gigalitres of water during next summer for $27 million, on top of the $607 million paid each year to keep the plant operational.

The algal bloom also threatens the annual tourist paydays of river towns over the coming long weekend and for Easter.

The Loddon River between Cairn Curran and Laanecoorie reservoirs, as well as the reservoirs themselves, are now blue-green algae declared. Blue-green algae outbreaks have also been declared this week on the Edward River at Moulamein and the Murrumbidgee River at Carrathool and Hay.

High algal levels have been detected in Lake Moodemere, near Rutherglen, and Sunday Creek. The public has also been warned to beware of using downstream sections of declared algae areas in the Murray as official warnings may lag due to testing needs.

GWMW has been topping up town storages and advised rural customers to “stockpile and store as much water on farm for stock and domestic needs as is possible,” although many said they had no warning of the shutdown.

GWMW has offered to cart 28,000 litres of water to rural customers for emergency household use. Victorian water authorities say towns supplied from treatment plants are assured safe water.

media_camera .

chris.mclennan@news.com.au

@McLennanCm