Fish are being affected by what is known as hypoxic blackwater, where oxygen levels drop due to bacteria sucking oxygen from polluted floodwaters.

Major flooding is still occurring at Echuca-Moama and other Victorian-NSW border towns after the Murray River peaked at record levels in October.

Yesterday, Environment Minister Susan Close said there was an increased likelihood of a blackwater event in South Australia.

Lower dissolved oxygen levels are already being recorded and warmer temperatures forecast for the coming week are likely to increase the risk.

Recreational fishing charity OzFish has deployed an emergency team to rescue the fish in partnership with state fishing regulators and the Murray Darling Basin Authority.

OzFish founder and chief executive Craig Copeland said groups had rescued 250 freshwater crayfish this week, with other teams deployed at other Victorian sites.

“Co-ordinating these collaborative rescue efforts is vitally important and we are proud to be playing a part alongside so many like-minded and committed individuals and their organisations,” he said.

“Given the situation affecting native fish we have a further Fish Emergency Recovery Team deploying from today to relocate as many native fish, including Murray cod, to safe water.”

A Bureau of Meteorology update on Friday said rainfall in October was the highest on record for large parts of the Murray-Darling Basin.

In the central west NSW town of Forbes, locals are waiting for the worst flooding in 70 years.

Emergency services have 22 emergency evacuation warnings out across the state including for Wagga Wagga, Gunnedah and Moama.

In Forbes, the overflowing Lachlan River threatens to rise above 10.8 metres, a mark not reached since 1952, with about 1000 people told to leave for higher ground.

The SES said support is on the way to communities in preparation of significant expected flooding.

“The ground that we’re standing on here will be inundated later today,” SES manager Ashley Sullivan said

Forbes Shire Council mayor Phyllis Miller said Radio floodwaters were “lapping on the back streets of the shops”.

“It’s pretty awful but it’s what we’ve expected,” she said.

The flood peak about 20 kilometres upstream of Forbes on Friday morning was expected to reach the township by evening, the Bureau of Meteorology said.

Emergency accommodation has been set up at a local school.

Local cattle farmer Charles Laverty spent Thursday sandbagging his property on the outskirts of Forbes, with about one third of his paddocks already underwater.

Continued flooding has hit the area and other farming communities hard, as they struggle to recover from repeated bouts of destruction to crops and livestock losses.

“A lot of (my neighbours) have given up on harvesting those areas, which is very expensive,” Laverty said.

“The losses are going to be devastating for them.”

Elsewhere, the Murrumbidgee River has caused major flooding and evacuation orders at Wagga Wagga.

The river reached 9.72 metres on Friday morning, above the December 2010 mark and on its way to a 1952 record by the evening.

Major flooding at Hay is expected to worsen from mid-November while moderate flooding is occurring at Tumut and Narrandera.

In the west, flood peaks are flowing into the Barwon-Darling River system, causing flooding at Mungindi, Mogil Mogil and Walgett.

Brewarrina, Bourke and Louth are among towns warned to prepare for major flooding, similar to that experienced in September 1998.

-with AAP