A sample site in the Lexia wetlands – between Melaleuca Park and Whiteman Park in Perth’s north-east – has gone from being a seasonal swamp to all dried up. It is one of several places where different species of frogs have stopped calling.

An annual monitoring report from this year stated without groundwater level rises, the distribution of some frogs would contract in the next three to five years, most in the middle and northern reaches of the Gnangara plan area.

Melaleuca, near Ellenbrook, was once home to the most northern habitat of the endangered black-striped minnow. But the wetland has gone from being full half the year with a small patch of water left in the summer, to having nearly no water at all.

The minnow is believed to be extinct at the site but persists in wetlands in the South West.

Banksia woodlands, a threatened ecological community of national significance, are declining in health around several wetlands.

Lake Gnangara, the most southerly of the Wanneroo wetlands, and Lake Mariginiup have become acidic after previously submerged soils containing metals and other sediments were exposed to oxygen because of dropping water levels.

High levels of acidity results in fewer invertebrates and, in the case of Mariginiup, the local extinction of the bluespot goby fish.

There is hope for Marginiup, which is one of the lakes where water thresholds are being increased and the acidification could still be turned around.

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Department of Water and Environmental Regulation principal water planner Michael Hammond worked on the new Gnangara plan and said the government was confident it would improve water levels for many wetlands.

“At some sites we’re able to achieve a recovery in groundwater level and an improvement in the ecological health of important sites,” he said.

“At other sites, where we’re currently seeing a declining groundwater, we’re able to achieve a stabilisation in levels and so a protection of the remaining ecological values, and in other sites where climate is the predominant factor in causing the declines we’re able to achieve a reduced magnitude of decline.

“Which means some of these ecosystems will have a better chance of adapting to the drying as they adjust over a longer period.”

But the new Gnangara plan will not be enforced all at once.

From September, residential bore users will have to reduce their number of garden watering days from three to two, saving 16.1 gigalitres.

But 30 gigalitres that goes into the Water Corporation’s public supply system will not be curtailed until 2028, alongside about 10 gigalitres of other licensed water.

The Gnangara management plan also notes almost all the groundwater resources it covers are over-allocated when it comes to self-supply water licences, and will still be over-allocated after 2028 until they expire and are renegotiated.

Ultimately, there will be 10 per cent less healthy wetlands if the plan is successful, compared to 36 per cent with no intervention.

Perth’s population is also projected to grow to 2.9 million people by 2031, and 3.5 million by 2050.

The increased water demand will be offset in large part to a new desalination plant – which turns seawater into freshwater but needs a lot of energy to do so – to be built in Perth’s north by about 2030.

DWER believes there has been a stabilisation of the mound in recent years and Water Minister Dave Kelly said it would take something drastic to change the new Gnangara plan.

“We’re confident that this will this plan will be robust for the next 10 years,” Kelly said.

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“This plan does make some significant changes ... if we implement them, we can still have a green, livable city. If we don’t, then the wetlands that we enjoy, the street trees that we currently value, those will be under threat.”

Hammond said as a shared resource, everyone needed to play their part in reducing groundwater use – and that started at home.

“Becoming more efficient with our water use, planting water-wise gardens, and if we all play our part, we can help ensure the long-term sustainability of Perth’s groundwater resources,” he said.