The extra water will add to already saturated rivers, which are currently flooding parks and further upstream on the Murray, causing road closures.

The Bureau of Meteorology predicts Swan Hill will receive up to 50mm of rain from this afternoon through to tomorrow evening.

A deep low pressure system moving across the south-east of the country is responsible and is expected to give about 80 per cent of Australia significant rain.

Bureau of Meteorology (BOM) meteorologist Sarah Scully said 20mm to 30mm of rain would create a minor flood warning for the Mallee, and beyond 30mm would constitute a full warning.

"Seeing as we're expecting 25 to 50 millimetres for the region, there's a good chance that will happen," Ms Scully said.

"It will be heaviest probably on Friday night, and into Saturday morning," she said on Wednesday.

In preparation for the weekend's forecast downpour, the Swan Hill SES unit’s Rob Merrett said volunteers were preparing sandbags and tarpaulins.

"It would be people who haven't cleared their spouts out might get flooding through the roof, and some inundation through low lying areas," Mr Merritt said.

"But if it's a slow and steady and constant build up (of rain) it should be fine," he said.

For more on this story, see Friday's edition of The Guardian (September 3, 2010).