From an Executive Summary of an Ecological Assessment for the planned development (p.1):
“From my observations, the ecological significance of the site relates largely to the presence of rare wetland plants and habitat for the endangered Blue-billed Duck. All 1.6 hectares of the dam is covered with native submerged plants, including rare species. Those plants underpin the aquatic ecosystem by forming the base of the food chain for the rest of the wetland organisms, from microorganisms to frogs, fish and waterbirds such as the Blue-billed Duck.
In addition, the treed vegetation on the dam’s northern bank is quite significant, ecologically and for landscape amenity. Several of the plant species growing there are rare – one of them rare throughout Victoria and others, within Knox.
Even before some of the site’s ecologically significant features were identified, the dam and the vegetation to its north were given the planning protection of Schedule 2 of the Environmental Significance Overlay (ESO2) in the Knox Planning Scheme. Because of that overlay and the broader Victoria Planning Provisions, any proposals for rezoning, development, works or vegetation removal on the site must be assessed for their impacts on ecological values.
Any residential development of the former horticultural research station will require a wetland system on the floodplain to manage stormwater. The existing dam could contribute to stormwater management but it would need modification. Modification would also be required to improve the public safety of the currently tall, steep banks on the south, west and east. Shores with more gradual slopes would also be ecologically beneficial.
The theoretical option of filling in the dam and constructing a new wetland system elsewhere would kill much of the vegetation on the northern bank. That is because the root systems of the eucalypts and some other species (including the locally rare Hairy Knotweed) are reliant on the presence of the water in the abutting dam. It would take decades to replace the existing habitat value. Such an outcome would conflict strongly with the objectives of ESO2.
Filling in any part of the dam will also cause the loss of the dense cover of significant submerged native vegetation, although it may be possible to transplant some of it to a new wetland. Losing the dam and its vegetation also means losing the habitat for all the dependent fauna, such as Blue-billed Ducks. It would take some years for a new waterbody to provide similar habitat value.”