OZCAST EP 7: What’s the go with flow? Why it's needed for native fish to thrive in Australia

In this episode of OzCast, we look below the surface of the flow of water in the Murray-Darling Basin as a critical factor that affects the health of the entire ecosystem and why it is fundamental for native fish. Iain Ellis, with 23 years in the management of fish production in the Murray Darling Basin, makes clear that flowing waters from the upper reaches to the lower stretches and mouths of rivers are critical for thriving fish populations.

He outlines that for more than 150 years, these waterways have been impacted by dams, weirs, regulation, diversion and land clearing all of which has changed the way water flows through rivers. This is what is meant by the term “altered flow regime”.

Efforts are ongoing to address this challenge, however, achieving a sustainable and equitable balance remains a complex and contentious issue, with ongoing debates and negotiations among stakeholders. However, the discussion Iain uncovers in this OzCast outlines that if the flow regime doesn’t suit native fish then complementary measures that target fish passage, stocking and habitat restoration are like band aids. He reminds us that the word complementary means “as well as”, and not “instead of” better flows. He suggests some emergency response activities such as fish rescues or re-stocking can also be tokenistic if they don’t address the actual problems that created the emergency situations threatening fish.

Essentially, Iain suggests that in many cases we’re taking two steps backwards for every small step forward and climate change will make this worse if we don’t deliver flow regimes to support fish breeding and survival year after year in our rivers.

Iain describes how habitat is not just about snags or rocks for fish. The way water moves through a fish's environment also influences its habitat. However, changed flow patterns and the construction of weirs and dams can lead to habitat loss, particularly for “flowing water specialist” native fish species that require specific flow conditions for breeding and survival. Every recreational fisher or local living along the Murray Darling Basin should tune into this episode, and you'll quickly discover why it's a must-listen.

Iain Ellis

Iain is a Fish Ecologist who has worked across the Murray-Darling Basin for more than 23 years. He has substantial experience in the planning and delivery of flow events o support native fish, the management of fish kills and hypoxic blackwater events, and threatened species conservation. Since 2019 Iain has been the Native Fish Recovery Strategy Coordinator for the Lower Darling – Baaka Reach.

This role involves coordination of activities which support native fish in the Menindee Lakes and Lower Darling-Baaka River – an area that experienced mass fish kills in 2018-19 and in 2023. Activities include aeration in disconnected waterholes in drought, rescue and relocation of stranded fish, temporary fish ladders weirs and community engagement and empowerment.

Iain has been involved in the planning of river flows to support native fish and their habitat across lowland (low gradient) rivers in the western parts of the Murray-Darling Basin. This involves the delivery of specific flow events to support breeding, dispersal (migration or movement to access key habitats) and recruitment of native fish. Iain has also led threatened fish conservation and recovery programs and has contributed to the conservation of the critically endangered Murray Hardyhead for over 20 years.

In regulated rivers, there are huge swathes of river/floodplain where the altered flow regime is impacting on fish stocks. It’s been happening for decades, and it’s getting worse as climate change leads to more and more competition for water and more extreme weather events which include droughts and hypoxic blackwater events from floods.

Iain notes that rec fishers should be concerned about ensuring appropriate flow regimes for fish above all else. If a variable flow regime is not maintained that supports fish in our rivers, s fish numbers are unlikely to recover.