Rainfall and temperatures in the Gunbower Forest and surrounding areas were close to the long-term average during 2020-21. Carryover of water in the Murray system was important to meet demands for water for the environment early in the water year. Allocations against high-reliability water shares in Victorian Murray entitlements to water for the environment, which are used to supply Gunbower Forest and Gunbower Creek, reached 55 percent in October 2020 and 100 percent in February 2021. Water for the environment was delivered to Gunbower Forest and Gunbower Creek in line with an average climate scenario in 2020- 21, and most planned actions were achieved.
Small peaks in the Murray River delivered minor inflows to Gunbower Forest via low-lying flood runners in July 2020. Another short peak in September 2020 was excluded from the forest by closing the regulators on the Murray River to prevent nuisance flooding of Yarran Creek. In late winter/spring 2020, water for the environment was used to fill Reedy Lagoon and Black Swamp within Gunbower Forest. Some of the water from Black Swamp spilled into wetlands within the Little Gunbower wetland complex. Other wetlands within Gunbower Forest were allowed to draw down during the first half of 2020-21, to reduce carp.
Additional deliveries of water for the environment in autumn 2021 topped up Reedy Lagoon and filled the Little Reedy wetland complex. The planned autumn top-up watering action at Black Swamp did not proceed, to allow the wetland to dry and hence reduce carp abundance ahead of a planned fill in winter/spring of 2021-22.
Fishway construction activities in Gunbower Creek limited deliveries of water for the environment to Gunbower Forest via the Hipwell Road Regulator in autumn and early winter 2021. Vegetation monitoring in autumn 2020 detected a slight decline in the condition of river red gums in some parts of the forest. Delivering water to selected wetlands and river red gum stands is proposed after the construction works conclude in winter/spring 2021, and more extensive floodplain watering in autumn/winter/ spring 2022 is a high priority to improve tree and understorey condition and provide habitat for native fish and waterbirds.
In Gunbower Creek, water for the environment was used to maintain access to habitat and food resources for native fish during winter 2020 (when irrigation flows cease) and to promote spawning and improve the quality of nursery habitats for native fish (especially Murray cod) during spring and summer. Construction of new fishways at Cohuna Weir and Koondrook Weir commenced in May 2021 and should be completed by August 2021. During the construction period, there will be little flow in Gunbower Creek, and pool habitats will be maintained downstream of the weirs to support native fish.
Annual fish surveys in Gunbower Creek have detected successful breeding and survival of Murray cod each year that water for the environment has been delivered, and the surveys are showing improvements in abundance and age structure within the resident Murray cod population over time. Freshwater catfish are also breeding in Gunbower Creek. Environmental flows will be necessary to help restore native fish habitat and support fish dispersal from the managed refuge pools once the fishway construction activities are complete. The fishways are expected to significantly improve the abundance and diversity of fish populations over time by allowing fish to move between Gunbower Creek and the Murray River. This will enable fish that successfully breed in Gunbower Creek to migrate into the Murray system and for species (such as golden perch and trout cod) that breed elsewhere to move into Gunbower Creek to feed and develop. Greater fish movement into and out of Gunbower Creek will help to grow populations of native fish within Gunbower Creek and across the broader region.
