A $650 million dollar project to expand Wyangala Dam is underway to improve water security and drought resilience in the Lachlan Valley.
The project, part of the $1.1-billion dam building package announced by the federal and NSW governments last October, will see the dam wall raised to increase Wyangala's storage by 53 per cent, creating capacity for an additional 650 gigalitres.
It has been described by NSW Water Minister Melinda Pavey as "once-in-a-generation" infrastructure.
However, landholders in the middle and lower Lachlan are concerned the fast-tracked project could have a dire environmental impact and reduce the availability of groundwater.
WaterNSW confirming that while work on the project will begin in October, the first draft of the Environmental Impact Study will not be made public until mid-2021.
Booligal grazier, Hugh McLean is a member of the newly formed Lachlan Floodplain and Wetland group.
He said the group's main aim was to see that the project's business plan, hydrology report and environmental impact statement were made public before work on the dam began.
"The biggest concern from the environmental side is the capturing of the one in seven years or one in ten year flood events," Mr McLean said.
"At the moment those flood events would flow through the system and go into major wetlands at the bottom of the river.
"The Great Cumbung Swap and the Booligal Wetlands are both of national significance, the Booligal Wetlands has one of the largest ibis breeding rookeries in Australia."
He said they were also concerned that reducing overland flood events would diminish the ability for groundwater to replenish in the Lower Lachlan.
"A lot of the groundwater recharge comes from overland flooding, so if you capture those events within the dam what happens to recharging the aquifer?"
A Middle Lachlan member of the group, Mal Carnegie added the lack of consultation by the government thus far on the project did not pass the pub test.
"It's either negligent, deliberate or both and it's very concerning either way," Mr Carnegie said.
"The proposal represents a step-change for the hydrology of the whole Lachlan catchment, further disconnecting the river and floodplain."
He said the project would have economic, social and environmental impacts, and he was particularly concerned by its effect on Lake Cowal.
"Lake Cowal is NSW's largest natural inland lake, it's an important breeding area for a range of waterbirds and feeding ground important migratory birds," Mr Carnegie said.
"The flooding cycle for Lake Cowal is heavily reliant on floodwaters coming in from the Lachlan."
Were other alternatives considered?
Fergus McLachlan, Tupra Station, Oxley added that the government had not offered any other alternatives for improving water security in the valley.
"We've heard nothing of any alternate efficiencies methods, it seems to be this or nothing," Mr McLachlan said.
"Building a bigger dam doesn't put more water in the system, instead the water we do have should be used more efficiently so there's more water to go around."
He said while the dam expansion was good for towns upstream, it was a disaster for those downstream, both in terms of water quality issues and the environmental impact.
"Our water quality now is so bad that some people can't shower in it," Mr McLachlan said.
"And if you called the Great Cumbung Swamp the Great Cumbung Barrier Reef everyone would be screaming their heads off but because it's called a swap it doesn't grab people's attention."
Ms Pavey's office stated that the Wyangala Dam wall-raising project was identified in the Lachlan valley water security study as the preferred key strategic measure - along with initiatives such as the proposed Lake Rowlands to Carcoar pipeline - intended to enhance water security in the region.
Construction work to begin months before environmental report is made public
The Lachlan Floodplain and Wetland group met with federal Environment Minister Sussan Ley on Tuesday to voice its concerns.
Ms Ley stated that the matter falls under the Environment Protection and Biodiversity Conservation Act and must undergo full assessment.
"I am committed to meeting interested parties, in particular those that live and farm in the area, so that when I am presented with the final report for my determination I can have a greater sense of context of the issues involved," Ms Ley said.
Water NSW stated the wall-raising project was in its early stages, involving community engagement, early scoping works, development of a concept design and the final business case, as well as the commencement of an environment impact study.
It said the environmental impact study's first draft would be made public in mid-2021.
The project's first major construction work is the relocation of the Reflections Holiday Park, which is scheduled to begin in October, and is estimated to take up to 12 months.