Australia's most recent strong La Nina event in 2011 brought huge floods to the region, inundating Rochester, and areas around Boort, Charlton, Bridgewater, Loddon and Baringhup.

The Bureau of Meteorology has La Nina alert active, indicating a 70 per cent chance of the weather system forming.

La Nina typically brings increased rainfall, cooler daytime temperatures and warmer overnight temperatures.

2011 flood coverage:

Central Victorian water management agencies say they hope for a fine balance between much needed rain and unwanted floods.

North Central Catchment Management Authority floodplain manager Camille White said the organisation was better prepared than in 2011.

Ms White said the organisation was already preparing internally for floods, training and practising liaising with other agencies.

"Flooding in our region was pretty devastating, party because we didn't have the information to warn communities about what might happen," Ms White said.

"We've got better data. We've got municipal flood emergency plans."

Ms White said about half of La Nina events in the last 100 years had caused flooding in the north central region, so it could bring floods this year but it wasn't definite.

Coliban Water climate and population adaption executive general manager Steve Healy said high rainfall was a good thing for the organisation, after a series of dry years.

Mr Healy said the Upper Coliban Reservoir could spill into the Lauriston Reservoir if it rained heavily, and onward, but that would be good for the river system.

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He said Coliban Water was in a much better position than during the 2011 floods, with preparations such as a flood wall around the Rochester Water Treatment Plant.

Mr Healy said Coliban Water had run through preparedness testing and communications with other agencies in recent weeks.

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He said Coliban Water staff hoped for good rainfall, but would believe it when they saw it.

"We're still at the mercy of natural environment and natural events," he said.

Goulburn-Murray Water River operations manager Andrew Shields said good rain would help replenish Lake Eppalock and Cairn Curran, both below 50 per cent capacity.

Mr Shields said the BoM outlook of likely rain was good news for catchments across northern Victoria.