Selected Area: Lachlan

The Lachlan River flows through the lands of the Nari Nari, Ngiyampaa, Wiradjuri and Yita Yita Nations, forming part of Songlines and Dreaming tracks. It has provided food, shelter and resources to Aboriginal people for between 40,000 and 65,000 years. The Lachlan supports a diverse range of landscapes and species that vary enormously through extremes of weather conditions. Our work here is focusing on monitoring the outcomes of environmental water in the lower Lachlan river system, from Lake Brewster to the Great Cumbung Swamp.

Image: Great Cumbung Swamp in flood. Photo credit: Will Higgisson

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We are honoured to work on the ancestral lands of the Nari Nari, Ngiyampaa, Wiradjuri and Yita Yita Nations People. We recognise their unique ability to care for Country and their deep spiritual connection to it. We honour Elders past and present whose knowledge and wisdom has ensured the continuation of culture and traditional practices. We are committed to genuinely partner, and meaningfully engage, with Traditional Owners and Aboriginal communities to support the protection of Country, the maintenance of spiritual and cultural practices and their broader aspirations in the 21st century and beyond.

About the Lachlan River

Following white settlement, the Lachlan and the towns along it, became enshrined in the poems of Henry Lawson and Banjo Patterson. It epitomises much of what we romanticise about the Australian bush – it is the land of Clancy and of droughts and flooding rains.

Black box (Eucalyptus largiforens) on the edge of Booligal Wetlands. Photo credit: Fiona Dyer

Although our town hasn’t got
The name of quite a lovely spot –
You see I live in Booligal…..
We prayed that both in life and death
Our fate in other line might fall,
O send us to our just reward
In Hay, or Hell, but gracious Lord
Deliver us from Booligal.
And the people here have an awful down
Upon the district and the town –
Which worse than Hell itself they call;
In fact, the saying far and wide
Along the Riverina side
Is “Hay, Hell, and Booligal”.

– Banjo Patterson

The river rises near Gunning (just north west of Canberra) and travels some 1400 km to its terminus in the Great Cumbung Swamp near Oxley in NSW. It is the fourth longest river in Australia and, for the most part, it is disconnected from the rest of the Murray-Darling Basin, connecting to the Murrumbidgee River only during large flood events.

The river system supports a diverse range of landscapes and species that vary enormously through extremes of weather conditions. During long periods of dry, the landscape is parched, wetlands are dry and the river sits low in the channel exposing deep clay banks. During flood, there are wide expanses of water across floodplains, wetlands, and ancient river pathways. It is during the floods that the landscape comes alive with an extraordinary diversity of birds and other fauna. Significant bird breeding events occur in the wetlands of the Booligal Swamp, Lake Cowal and the Great Cumbung Swamp. Plants long dormant come to life and the small wetlands across the landscape become refreshed providing Black box and River red gums with the water that enables them to persist through the next dry period.

Why this area is important?

The Lachlan river system has fundamentally changed through the building and operation of dams, and the use of water, mainly for irrigated agriculture. This has changed the flow patterns of the river and has substantially changed the inundation of wetlands. Most of the small and medium sized flow pulses which would have occurred naturally in the river in response to rain in the catchment, no longer occur as flow from these is captured by dams. This means many of the wetlands, billabongs and anabranches get water in them far less frequently than they would have before the dams were built. In addition, floodplain development, and structures on the floodplain affect natural flooding regimes. It also means that less water makes its way to the Great Cumbung Swamp.

Many native species, including fish, birds, and plants depend on certain flow conditions for breeding, dispersal, and reproduction. Changes to the way water moves and is used within the Lachlan river system has markedly altered the character and condition of the rivers, floodplains and wetlands, particularly those at the end of the river system (the terminal wetlands).

Environmental water is used in the Lachlan river system to support the significant ecological values that occur across the catchment, particularly those most affected by changes to flow regimes. Our monitoring focusses on the lower Lachlan river system from Lake Brewster to the Great Cumbung Swamp. Our research is based within the Great Cumbung Swamp which is a priority under the Basin Plan.

Image credit: Alica Tschierchke

Our approach

The Lachlan River exhibits extreme variability in flow; no two years are the same. This means that long-term data sets are vital in assessing the ecological responses to environmental watering and climatic conditions which are occurring in the Lachlan river system. Over the next three years, our team will be undertaking field sampling across the lower Lachlan river system as part of the Flow-MER program. We will continue to build on the five years of data collected during LTIM and further build our research on the response and requirements of the biota for watering.

Collection of field data

Our team collects on-ground data on stream metabolism and water quality, the diversity and condition of floodplain and wetland vegetation, and adult and larval fish community. Some of our field data are from loggers (for example water quality loggers which record dissolved oxygen and temperature in the river continuously) but most are from a series of field campaigns. These data are designed to detect ecological responses to flow.

Image: Vegetation monitoring at Whealbah in 2019. Photo credit: Will Higgisson

Analysis of data to link ecological response to flow

We analyse the ecological data we collect in relation to flow in the river and environmental flow actions. This is considered in the context of the prevailing weather conditions, land management and previous conditions at a site. This is used to evaluate the outcomes from the use of Commonwealth environmental water.

Image: Fish monitoring at Wallanthery. Photo credit: Mal Carnegie

Communicate our findings

We share our findings with our team, with the CEWH and with the broader community. We use a mix of reports, newsletters, media, presentations and conversations with people who are interested. We love to talk about our work! We also try to incorporate local observations into our knowledge base.

Image: Dr Joanne Lenehan, Senior Environmental Water Manager, DPE Environment and Heritage Group speaking at the Mt Boorithumble Engagement Weekend. Photo credit: Mal Carnegie

Conduct research

We undertake research that improves our understanding of how plants and animals respond to the flow regime so we can refine future environmental watering actions. Our focus during the Flow-MER program is to better understand how reed beds respond to water.

Image: Reeds in the Great Cumbung Swamp. Photo credit: Fiona Dyer

Aerial view of Straw-necked ibis colonies in 2016.
Photo credit: Will Higgisson

Current activities

We monitor a set of indicators to answer questions about what Commonwealth environmental water has achieved within the Lachlan river system.


We use flow data and information from water accounts to determine the contribution of Commonwealth environmental water to changes in flow and water level in the river system. This information underpins our analysis of the ecological responses to changes in flow.

Hydrology graph of Lachlan River. Image credit: Fiona Dyer et al., 2019

Stream metabolism and water quality

The energetic base of food webs in freshwater ecosystems is provided either by primary production (the energy fixed by photosynthesis occurring in plants and algae) or by breakdown of organic matter such as leaves, wood and organic carbon dissolved in the water. Collectively these are known as stream metabolic processes.

We use continuous measurements of oxygen concentrations in the river at 4 sites in the lower Lachlan river system to provide information about primary production and organic matter breakdown and how it is modified by the use of Commonwealth environmental water.

Lachlan River at Whealbah. Photo credit: Will Higgisson

Diversity of floodplain and wetland vegetation

Floodplain and wetland plant communities provide food and habitat for water birds, amphibians, fish, terrestrial vertebrates and a variety of other biota and support breeding events for tens of thousands of colonial nesting waterbirds. Water plays an important role in supporting these plant communities across the lower Lachlan.

We monitor floodplain and wetland plants at 13 sites across the lower Lachlan catchment in spring and autumn to understand how the plants have responded to the use of Commonwealth environmental water.

River red gum seedling after flooding. Photo credit: Laura Caffrey

Adult and larval fish communities

Fish are an iconic part of our river systems and are a valuable indicator of aquatic ecosystem health. Supporting native fish in the Lachlan river system has been a major focus of environmental water delivery over the past five years. Water has been used to support fish outcomes, either directly (through the provision of spawning flows) or indirectly (through improvements to water quality or habitat access) in every year of the program.

So far monitoring fish monitoring has spanned 20 sites along nearly 500 km of river between Forbes and Hillston, with the focus of sampling being 10 sites between Wallanthery and Hillston. Each year, the focal reach is sampled between March and April. We also monitor larval fish more intensively at three sites in the same reach fortnightly between October and December each year. This information is used to determine the role of Commonwealth environmental water in both fish breeding and in supporting the populations.

A big Murray Cod from Lake Cargelligo in September 2019. Photo credit: Robin Carter

Communication and engagement

Our team are engaged in activities across both the lower and mid Lachlan catchments to communicate our work and engage interested locals in our program. Our activities include sharing the learning and results from project activities through workshops, field demonstration days in local communities to observe the MER team in action, environmental education events, Citizen Science projects and training, local newspaper articles and community websites, newsletters, web and social media. We also contribute to on-going adaptive management associated with environmental watering and foster opportunities for collaboration among core stakeholders so that the value of using of public funds for monitoring, evaluation and research in the Lachlan Selected Area is optimised.

Mt Boorithumble Engagement Weekend. Photo credit: Mal Carnegie


During the MER Program, we will be conducting research to develop techniques to monitor the response of reedbeds to environmental water. The reedbeds of the Great Cumbung Swamp are an important asset in the Lachlan catchment. They have been targeted with environmental water over the past five years but have not been monitored because of the challenges around site access. With the emergence of a range of new technologies, including drones and high-resolution satellite data, there is an opportunity to develop techniques to monitor the reedbeds that are practical and cost effective. This research will help us understand the key indicators of condition for reedbeds that can be measured easily, and cost effectively using remotely sensed techniques and develop an appropriate monitoring program for Common reed (Phragmites australis) and Cumbungi (Typha domingensis) and their response to watering.

Reeds in the Great Cumbung Swamp. Photo credit: Fiona Dyer

What we’ve learned

Over the past five years, we’ve learnt a lot about delivering water in the Lachlan catchment. Water management has become more agile and responsive to catchment conditions and field observations, and there are now more effective processes and strong relationships in place to support the use of water than when we started in 2014.

Between 2014 and 2019, a total of 122 208 megalitres (ML) of Commonwealth environmental water was used strategically in the Lachlan river system to support environmental outcomes. Annual volumes delivered have been as low as 5,000 ML in 2014-15 when conditions were dry, and in years of greater water availability (2015 – 2018), the volumes used have been between 30 000 ML and 36 000 ML.

The volumes of Commonwealth environmental water used have been a very small proportion (typically less than 5%) of the annual flow at Forbes, but has been a far more significant proportion of the flow at Booligal, with more than 40% of the annual flow in the river at Booligal in 2015-16 and 2017-18 provided by Commonwealth environmental water. This illustrates the relative importance of Commonwealth environmental water for maintaining variable and ecologically significant flow regimes in the lower reaches of the Lachlan river system, compared with the almost negligible contribution in the mid Lachlan.

Native fish outcomes

Commonwealth environmental water has typically been used in spring providing native fish outcomes and improvements to habitat quality and access. Water has also been used opportunistically to support bird breeding and to mitigate adverse water quality outcomes during the floods of 2016-17. In 2017-18 and 2018-19, small winter freshes* have been delivered to the lower river system to provide flow variability and habitat access during the winter months when flows are operationally low.

  • A fresh is a temporary in-channel increased flow in response to rainfall or release from water storages.
Image: Freshly collected sample from a larval fish drift net set overnight at Wallanthery. Photo credit: Mal Carnegie

Watering wetlands

Within the main river channel environmental flows have sought outcomes ranging from hydrological connectivity and variability, improvements in dissolved oxygen concentrations, providing cues for native fish spawning and providing refuge habitat. A number of significant wetlands have also received water for the environment including Booligal, Lake Tarwong and the Great Cumbung Swamp. These wetland flows have sought to support waterbird breeding, vegetation condition and fish dispersal outcomes.

Image: Pelicans at Lake Bullogal. Photo credit: Dr Joanne Lenehan, Senior Environmental Water Manager, DPE Environment and Heritage Group.

Bird breeding

The cooperative management of water levels between the CEWH and NSW enabled 9,000 ibis chicks to survive to fledgling stage in the Booligal wetlands in 2016-17. Without the involvement of Commonwealth and NSW environmental water these chicks would have died. This result supports our finding that small amounts of water can be used very effectively to achieve site scale benefits.

Image: Juvenile birds in 2018. Photo credit: Dr Joanne Lenehan, Senior Environmental Water Manager, DPE Environment and Heritage Group.

It’s not all about ‘adding water’

  • To achieve outcomes for fish sometimes requires that flow is managed in combination with water temperatures. Water that is too cold or too hot, even if it is at the right level of volume, will fail to support successful spawning or migration.
  • Water levels are critical for bird breeding and in 2016-17 very small amounts of Commonwealth environmental water were used to maintain water levels to support chicks to fledging stage. Once fledged these birds become part of the overall bird population seeking refuge and habitat along the Lachlan and surrounding river and wetland systems which is supplemented by water for the environment.
  • Land management is critically important – grazing and the impact of feral animals is limiting some of the outcomes that might be achieved by environmental water in some places.
  • While natural flow variability is the dominant driver of patterns of water quality and stream metabolism in the Lachlan River, water for the environment can generate smaller, but ecologically meaningful responses.
  • The effects of environmental water are likely to be more important in dryer years (e.g. 2014-15), where carbon has accumulated on banks and in flood runners.
  • In 2018-19, our monitoring showed that the strategy of managing Commonwealth environmental water to generate a number of small freshes had benefit for small bodied fish by generating a series of small pulses in production at the same time as the Flatheaded gudgeon were spawning.
  • Commonwealth environmental water can be used to maintain the diversity of native aquatic plants and the condition of long-lived tree species which depend on flooding.
Image: Groundcover vegetation during flooding in red gum woodland behind the Great Cumbung Swamp. Photo credit: Damian McRae

Environmental DNA

Environmental DNA (eDNA) can detect fish species presence by collecting and counting tiny fragments of DNA by filtering and analysing river water. This technique has been trialled in the Lachlan River at 18 sites between Forbes and Hillston (some 500 + river kms), to determine if it could complement conventional sampling of native fish communities. eDNA was able to detect a couple of rare species (Silver perch and Freshwater catfish) in the lower Lachlan River that conventional monitoring did not pick up. This study concluded that eDNA would be a great complementary technique at monitoring species presence at the larger scales, which can help inform the efficacy of environmental flow programs across years.

Image: Portable filtration equipment for processing water samples for eDNA extraction. Photo credit: Rheyda Hinlo

Larval fish growth

Early life as a fish is hard going, you need the right conditions to survive and grow, and sadly many larvae just don’t make it! To help support these early life stages, flows are often put down the river to boost food resources, but the link between food resources and larval fish growth needs to be better understood. In an attempt to help understand this relationship, larval fish earbones have been analysed to determine if there is a link between stream productivity (the start of the food chain) and larval fish growth. Data collected over the past five years suggests that when stream productivity increases, we see an increase in larval fish growth.

Image: Larval Murray Cod captured from the Lachlan River photographer: Hugh Allan

Image caption: Floodplain vegetation responding to water – Whealbah 2016. Photo credit: Fiona Dyer

Our team

A/Professor Fiona Dyer, Selected Area lead

Fiona is interested in understanding how freshwater systems respond to natural and anthropogenic variations in flow with a view to informing decision making in water and land management.

Ben Broadhurst, Larval fish theme lead

Ben is a fish ecologist with a background in population monitoring and spatial ecology of freshwater fishes. Ben has a strong interest in conservation and management of native fish and mitigating threatening processes.

Dr Jason Thiem, Adult fish lead

Jason is a Fisheries Scientist with the NSW Department of Primary Industries. Jason’s current research program is focussed on the abiotic drivers of fish movement, spawning and recruitment within the Murray-Darling Basin, with a strong focus on riverine connectivity.

Dr Will Higgisson, Vegetation theme lead and research lead

Will is a plant ecologist, with a background in the conservation and management of aquatic and wetland environments. Will is interested in understanding how floodplain and riparian plants respond to changes in river flow patterns related to water resource development, climate change and environmental water.

Professor Ross Thompson, Stream metabolism theme lead

Ross is a freshwater ecologist, interested in the study of aquatic biodiversity, ecosystem function and food web ecology. Ross is the director of the Centre for Applied Water Science, University of Canberra.

Dr Joanne Lenehan, Senior Environmental Water Manager, DPE Environment and Heritage Group, Communication and engagement lead

Jo is the Senior Environmental Water Management Officer for the Lachlan River system. She is interested in how good science, local and traditional knowledge, and communication enables adaptive management of water-dependent ecosystems and community values.

Dr Kate Brandis, Waterbird theme lead

Kate is from the Centre for Ecosystem Science, UNSW. She is a wetland ecologist who specialises in waterbirds, waterbird breeding and maximizing environmental flows for positive waterbird outcomes.

Alica Tschierschke

Alica is an ecologist with an interest in conservation land management, spatial data analysis using ArcGIS and data management.  She is a licensed drone pilot and is developing approaches to analysing drone data.

Dr Adam Kerezsy

Adam is an aquatic ecologist  and author of many scientific papers and the natural history book Desert Fishing Lessons: Adventures in Australia’s Rivers. Adam’s primary interest is the ecology of rivers and springs in inland and central Australia.

Rhian Clear

Rhian is a Research Assistant with a background in conservation, ecology and movement of freshwater native fish. Rhian has a strong interest in the management and protection of threatened native fish.

Ugyen Lhendup

Ugyen is a Research Technician involved in monitoring native fish population, collecting water quality data, monitoring vegetation, bioassessment and analysing water quality and macroinvertebrate data. He has an interest in conservation and land management.

Hugh Allan

Hugh is a fish ecologist with interests in threatened species conservation and spatial ecology.

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