Lakes and wetlands that rely on Perth's Gnangara groundwater system are set to dry out even more with WA's water regulator poised to grant the Water Corporation a massive allocation from the aquifer.
After two years in which the Water Corporation has been given close to or its maximum possible allocation of 165 billion litres from Gnangara, it is understood the utility could receive almost 140 billion litres next year.
The corporation last month applied to the Department of Water for 139 billion litres - 19 billion litres more than what is deemed sustainable.
With public submissions on the corporation's bid now closed, a decision from the department is expected soon.
The corporation's Gnangara licence requests, which are determined by Perth's dam levels, are generally upheld by the department given their importance to safeguarding Perth's drinking supplies.
The latest bid by the corporation comes after one of Perth's driest winters on record - when just 27 billion litres flowed into the dams - and despite moves to fast-track the expansion of the Binningup desalination plant.
Greens MLC Alison Xamon said it was "disappointing but entirely predictable" that the Water Corporation had asked for so much water from Gnangara given the utility's continued over-reliance on the aquifer.
She said that though the latest request was notably lower than in recent years, it was still far too high and risked doing "irreversible damage" to fragile wetlands that relied on the system.
"Twenty billion litres (above the sustainable limit) is still a significant amount of water and I don't think it's wise to underestimate that," Ms Xamon said.
"The sooner that we get down to sustainable abstraction levels the better."
Urban Bushland Council president Mary Gray said Gnangara's network of aquifers sustained ecosystems all over Perth and many were under stress because of its falling water levels.
"It's a major concern," she said.
Ms Gray said that per-capita water consumption in Perth was too high and contributed to Gnangara's woes.
She suggested major users of the aquifer, such as agriculture, be held to greater account.
(139 billion litres from the Gnangara aquifer) risked doing "irreversible damage""Greens MLC *Alison Xamon *