The 'Enhancing our Dandenong Creek' program and Dwarf galaxias

The 'Enhancing our Dandenong Creek' program and Dwarf galaxias

18.05.2015 - Posted by Amanda Shipp
There are very few urban natural resource management projects that show how an intervention can not only halt decline in ecological health, but actually improve it. The Enhancing our Dandenong Creek program is one such project, with major benefits for the native Dwarf galaxias.

A pair of Eastern dwarf galaxias (fish)

A pair of Eastern dwarf galaxias (source:
Fishes of Australia)

Melbourne Water is the responsible authority for 8400km of Melbourne’s waterways, including Dandenong Creek and Melbourne’s major sewerage pipe system. Melbourne Water and the Environment Protection Authority (EPA) are working in partnership to improve the health of Dandenong Creek through a five year program consisting of four different projects known as ‘Enhancing our Dandenong Creek’ (EODC). The EODC program includes a range of projects that look at protecting the creek from pollution, improving its natural amenity, creating new habitat for threatened native fish, and mitigating uncontrolled spills in the area.

Following an investigation in Dandenong Creek, it was found the Emergency Relief Structure (ERS) didn’t comply with EPA policy. An ERS is an outlet within the sewerage system that will overflow into the drainage system when the sewerage system is filled above capacity. This normally happens in a heavy rainfall event due to illegal stormwater connections and infiltration, which fill the sewerage system beyond capacity. By the time it overflows into the creek during high rainfall events, it is highly diluted and predominantly stormwater. The purpose of an ERS is to ensure that diluted sewage does not normally spill onto a person’s property (see Melbourne Water's Sewer Spills video on YouTube).

A traditional response to this would be to construct a duplicate sewage pipe. However, research along Dandenong Creek found that even though the ERS didn’t comply with the EPA policy, the wet weather sewage spills were not a significant cause of pollution in the waterway. Key pollutants identified were heavy metals and chemicals from the drainage system, which present significant stressors on the ecosystem. In light of this, the EPA have agreed to defer the construction of a new sewer and work in partnership with Melbourne Water to assess, develop and design a program to protect public health and reduce pollution while enhancing the surrounding natural amenity.

As part of this project, Rhys Coleman at Melbourne Water is developing a plan to support the Dwarf galaxias (Galaxiella pusilla), a nationally threatened native fish that was once common and widespread in the area. Rhys aims to improve habitats using his extensive knowledge of Dwarf galaxias requirements - based on his own research at the University of Melbourne, and supplemented by a team of consultants including Alluvium.

The Dwarf galaxias has a natural range across southeast Australia. They are small freshwater fish (usually less than 40 mm in length) that live in slow moving, shallow freshwater habitats, such as wetlands, billabongs and small streams that contain dense aquatic plants. With a mostly annual lifecycle, a critical ingredient for their success is an ability to move between multiple sites along a waterway corridor (primarily during floods) to help sustain population numbers across habitats with varying spawning success from one year to the next. An interesting adaptation of Dwarf galaxias to the variable Australian climate is an ability to cope with short periods of habitat drying. During these times, they are able to survive in moisture pockets such as underneath vegetation, leaf litter or in crayfish burrows.

A project site, wet in September 2014 
A project site, dry in February 2015

Habitat drying at one project site, in September 2014 (top) and February 2015 (bottom)

My main role in the project is to understand the hydrology and water balance at each site, and to identify minor changes to former floodplain habitats that can be made to ensure there are appropriate water conditions for Dwarf galaxias. Visiting the potential habitat sites and seeing the quality of aquatic vegetation, water conditions and even some Dwarf galaxias larvae at one site, reinforces the incredible potential of this project.

We look forward to seeing the project progress and the re-establishment of a healthy and sustainable native fish population within an urban environment.