Improving fish passage in Dandenong Creek
A new fishway has been built to support native fish to swim more freely between Port Phillip Bay and the waterways of the Dandenong Creek catchment.
Maintaining in-stream connectivity is critical for fish
Some of our native fish species migrate between fresh water and the sea in order to spawn and reproduce. Stream connectivity and habitat diversity are critical components of healthy rivers and creeks and fish require free movement along the length of rivers and streams and between estuarine and freshwater environments.
Impeding fish passage through the construction of dams, weirs, floodgates and waterway crossings can negatively impact native fish by interrupting spawning or seasonal migrations, restricting access to preferred habitat, increasing susceptibility to predation and fragmenting continuous communities.
In-stream fish barriers at Pillars Crossing
In 1986 a weir and flow control structure was built in Dandenong Creek at Pillars Crossing, at the junction of Dandenong and Mordialloc Creek, to raise the level of water upstream and regulate flow. In 2008, fishways were constructed to allow migrating fish to bypass the weir, however these structures are now considered ineffective under most operational conditions. Native fish, which were once abundant in Dandenong Creek, have been impacted by in-stream structures such as these, becoming restricted in numbers or locally extinct. Changes in land use, invasive aquatic plants such as Alligator weed, predation by pest fish, and habitat loss, has also impacted native fish populations in this area.
A new fishway is required
In 2004, investigations found that the removal of barriers through the use of fishways would open up more than 180 km of fish habitat in the Dandenong Creek catchment and greatly benefit the distribution of native migratory fish. Four fish barriers were identified that either restricted or prevented fish passage. The weir and flow control structure at the Dandenong and Mordialloc Creek junction is the most downstream barrier and therefore the one that needed to be addressed first.
In January 2021, Melbourne Water commenced construction to replace the old fishway at Pillars Crossing with a new one. The purpose of the new fishway is to re-enable passage of the native migratory fish community in the lower reaches of Dandenong Creek, which flows into the Patterson River and into Port Phillip Bay. The project includes installation of a cone fishway to bypass the weir and installation of a downstream random rock fishway to raise the water at the fishway entrance.
“This is a very exciting project that we anticipate will increase the abundance of native fish populations moving through the Dandenong Creek catchment. The completed fishway will enable native fish species to freely move between Port Phillip Bay and the lower Dandenong Creek to spawn and complete their life cycles. The Australian Grayling is ‘threatened’ under the Flora and Fauna Guarantee Act 1988. It relies on brackish water when hatching as new larvae and then freshwater for the majority of its lifespan. This is just one example of species we are hoping to see thrive in future years.”
Patrick McCluskey, Melbourne Water
Are fish moving upstream?
To assess the functionality of the new cone fishway for passage of small-bodied fish, and since most important fish migrations occur in Spring and early Summer, monitoring will be conducted from September-December 2021. The three month timeframe enables time for a broad suite of fish to arrive at the site and a variety of river flow conditions to move through the fishway. The fish monitoring consists of sampling at the top and bottom of the fishway to see which fish are accessing and using the structure.
Exciting early monitoring results from November 2021 indicate that the cone fishway is already helping fish to move upstream. Fish caught above the fishway include Common Galaxias, Spotted Galaxias, Lamprey and surprisingly, nine juvenile Australian Grayling! Australian Grayling are listed as vulnerable under the Environmental Protection and Biodiversity Conservation Act (EPBC Act) and have not been detected in the Dandenong Creek before, so this is very encouraging news.
Completed fish monitoring results will be available at the end of Summer 2022, which will provide an indication of the overall effectiveness of the new fishway and any redistribution of species following the fishway construction.
WATCH: Time lapse video of fishway construction
Links to the Healthy Waterways Strategy – Dandenong catchment
This project supports the performance objectives in the Healthy Waterways Strategy by providing habitat connectivity for fish along major waterways through improving fish passage at Pillars Crossing in the Dandenong Creek Lower sub-catchment.