Restricting the amount of greenery growing beside the state's waterways will have a detrimental effect on the environment while failing to meet its goal of reducing bushfire threats, top waterway ecosystem scientists have warned.

Announced in January, the Andrews government policy limits vegetation along rivers and streams to a 10-metre-wide area each side of the waterway.

Wetlands ecologist Joe Greet in a waterway near Woori Yallock, where the banks have eroded due to a lack of vegetation. Credit:Simon Schluter

While initially targeting a lowland area between the Dandenongs and the Yarra Ranges, the six water scientists fear the policy will set a dangerous precedent for the management of the state's waterways and potentially the city's water quality.

"The policy was heralded to better manage bushfire risk while effectively managing environmental values. It does neither," Melbourne University wetlands ecologist Joe Greet said. "It's very poor policy from a conservation perspective."