The state does not consider platypuses to be rare or threatened but the International Union of Conservation Network declared it 'near-threatened' in 2016, prompting the first of several reviews in Victoria.

The government's Scientific Advisory Committee has found mounting evidence platypuses could be declared 'vulnerable' amid mounting evidence some Victorian populations have declined considerably, sometimes to the point of extinction.

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Australian Platypus Conservancy biologist Geoff Williams said platypuses were found throughout central Victoria but some populations are clearly healthier than others.

"The situation in most of the rivers in the north central area is very much in the balance," he said.

"In other words, there were declines in the past - certainly during the Millennium Drought when populations probably went down quite dramatically - we believe they are coming back but that some populations are still on a knife's edge."

Mr Williams said studies suggested healthier populations up-river on the Coliban, where water levels had historically been more stable than on the Campaspe, for example.

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Less stable water flows in the upper reaches of the Loddon River appeared to be linked to a "perhaps struggling" population, he said.

Mr Williams said more research was needed across Victoria before anyone could reasonably say whether the species could meet the guidelines to be deemed "vulnerable".

"The key issue, we have to stress, is that a lot more information is needed and that will be critical to any scientific assessment about what is going on," he said.

The North Central Catchment Management Authority is responsible for river systems throughout central Victoria and project manager Darren White said environmental water flows have helped platypuses recover since the Millennium Drought.

That included releasing "autumn fresh" flows timed to allow juvenile platypuses cover as they left home for the wider world," he said.

"If they have a low river when they try to make that move they are open to predation from foxes. You want plenty of water around them at that time of year to keep them safe."

On the Campaspe, water is allowed to drop low sometimes to encourage water bug populations to surge.

"Then there's plenty of food for lactating platypuses, who have to eat something like 80 per cent of their body weight every day," Mr White said.

The tricky part was spring environmental flows, he said. Release too much water platypuses could be left without shelter from predators in their nests, too low and they could be vulnerable when they crawled into and out of the water.

"We've got to manage that the whole way through," Mr White said.

The catchment management authority has also been working on major river restoration projects including removing willows, restocking banks with native vegetation and helping farmers fence paddocks to keep livestock out of the water.

"All these things will help platypuses survive and, in some areas, to thrive," Mr White said.

Mr Williams encouraged people to report sightings to citizen science website the Australian Platypus Monitoring Network.