MOST Victorian rivers require more snags to improve health and increase fish numbers, according to a new survey.
The Department of Environment and Primary Industries counted the snags in 27,700km of rivers, using aerial photography and on-ground mapping.
"Our modelling shows the amount of woody habitat in our rivers was an average of 41 per cent below natural levels and we know that is having a significant impact on freshwater fish species," DEPI fish ecologist Zeb Tonkin said.
However, in the 1970s and '80s governments funded the clearing of creeks and rivers of fallen trees and branches because they blocked water flows, particularly during floods.
Governments funded stream improvement trusts administered by local councils.
The DEPI survey found areas needing most re-snagging work included the southwestern floodplains, Glenelg and North Central floodplain river regions.
In comparison, the Alpine, North East Uplands and East Gippsland Upland regions were in relatively good condition, Mr Tonkin said.
The Government will use the survey to prioritise areas for restoration. Snags will be put back and riparian zones revegetated.
"We know that numbers of threatened native species such as Murray cod do increase in response to habitat restoration and the same applies to many other native species," Mr Tonkin said. "In the past snags were removed from our rivers because it was incorrectly thought that they reduced flows and contributed to flooding."
Research has since shown snag removal has minimal impact on flood mitigation, impairs river stability and affects the health of our streams, such as reducing fish populations.
"Over the past 20 years we have been gradually returning snags to our waterways particularly through the efforts of Catchment Management Authorities," Mr Tonkin said."
Environment Victoria chief executive Kelly O'Shannassy said many of the state's rivers and streams had been treated as drains and now they were being properly considered as functioning eco-systems.