Australia

Wed Feb 25

Climate change is drying out the ‘forgotten rivers’ that keep the Murray-Darling alive. We need a new plan

Written by Avril Horne, Research fellow, Department of Infrastructure Engineering, The University of Melbourne

If you stand beside Seven Creeks in Victoria or Spring Creek in Queensland, they might seem small and unremarkable. But these creeks flow into the mighty Goulburn and Condamine Rivers, and punch far above their weight.

Small headwater creeks, at the beginning of a river network, act as the first source of water for bigger rivers. Headwaters deliver the first cool winter flows and the large seasonal pulses of water that trigger fish migration, setting the river’s rhythm. But they’re also the first to suffer from drought, heatwaves and water captured by thousands of small farm dams.

As the rivers of Australia’s largest system, the Murray-Darling Basin, experience a hotter and more variable climate ^[1], their headwaters are at the forefront of change.

This year, the Murray-Darling Basin Authority is reviewing the basin plan ^[2]. The plan sets sustainable, legally enforceable limits on water usage, and rightly identifies climate change as a central challenge. Yet its new discussion paper ^[3] pays surprisingly little attention to the vast network of smaller tributaries that feed the basin’s larger rivers.

We need attention on these “forgotten” rivers and streams, which are increasingly central to the survival of the Murray-Darling Basin as a whole.

The Basin’s blind spot under climate change

The discussion paper focuses on the big-name river systems in the basin, such as the Darling (Baaka) River in the north and heavily regulated rivers in the south such as the Murray, where big dams, barrages and diversions shape almost every drop of water.

This omission reflects how the original plan was conceived, and then in released 2012. Environmental priorities were defined around “priority assets”, such as major river reaches, internationally protected wetlands and refuges for wildlife where environmental flows were expected to deliver measurable ecological benefits.

This made sense when pressure from agricultural water extraction was the major threat. But this leaves out a huge part of the basin’s story.

Threading through the Basin are thousands of kilometres of small, so-called “unregulated” rivers and headwater streams. Historically, they were assumed to be relatively healthy because big dams were absent. But climate change is overturning that assumption. With declining rainfall and hotter temperatures, even small reductions in runoff can dramatically affect their flow.

Worse still, thousands of small farm dams scattered across the landscape are reducing ^[5] how much water flows through these waterways. More of these streams are now ceasing to flow for the first time, or remaining dry for longer. Climate change is amplifying every existing stress on smaller rivers.

If we are serious about preparing the basin for climate change, we can no longer overlook the springs and creeks which feed the system. These rivers are not peripheral – they’re central to its resilience.

How the warming climate is changing streams

Headwater streams may be small, but they form the ecological backbone of the basin’s rivers. These upper tributaries are biodiversity hotspots ^[6], supporting insects, frogs, fish and riverbank species dependent on regular flushes of water and cool, shaded habitats.

When these streams dry out, warm up or fragment into pools, these delicate ecological processes are disrupted. The effects stretch far downstream. Climate change is pushing these streams into more extreme boom–bust cycles ^[7], with longer, hotter dry periods punctuated by short bursts of intense rainfall. In small catchments, these shifts affect the entire flow regime: low flows become lower, and flooding becomes less reliable or arrives at the wrong time of year.

Headwater streams are known to be highly sensitive ^[8] to changes in flow. Under a drier climate these disruptions will intensify.

Climate change is drying out the ‘forgotten rivers’ that keep the Murray-Darling alive. We need a new plan

An aerial view of the receding waters of Lake Pamamaroo, part of the Menindee Lakes system, in 2019. Dean Lewins/AAP ^[9]

Can these changes be managed?

We can adapt to some degree. Rules limiting pumping from rivers during low flow periods, and better oversight of farm dams, can help keep water moving during crucial dry periods.

But when rivers are high, it’s a different picture. When river are full or even break their banks, it’s great for aquatic life. Fish move and breed, habitat is refreshed, nutrients moved downstream and wetlands rejoin the system.

Unregulated rivers lack the infrastructure, such as dams or barrages, to create or shape the big replenishing flows that ecosystems rely on, and climate change means these may simply happen less often.

If smaller rivers stop sending these floods downstream, larger rivers lose an essential part of their ecological rhythm.

Why this matters for the whole basin

What happens in the smaller creeks and rivers has a big impact. These small streams set the baseline conditions for the entire Murray–Darling system – from water quality and temperature to the timing of flows. When they falter, the effects are felt downstream.

The 2026 Basin Plan Review ^[10] offers us a chance to revisit its original assumptions. Focusing on major rivers once addressed the dominant sources of environmental decline, but under climate change, risk is no longer confined to those places.

If the basin loses its headwaters, no amount of downstream engineering can compensate. Bringing these “forgotten rivers” into climate planning isn’t optional — it underpins our environmental, cultural and economic future. Give me two