Monitoring conducted after natural floods in late 2016 detected a large population of carp in Gunbower Forest's wetlands. The carp were damaging wetland vegetation and causing high turbidity. To manage the impact of the carp, the floodplain and wetlands were intentionally left to draw down and dry after the natural inflows in late 2016, with no water for the environment delivered to the forest for the remainder of the 2016–17 year. The North Central CMA used the drying conditions to remove 1,170 kg of carp (mostly large adults) from Reedy Lagoon and Black Swamp.
Water for the environment was used to partially fill Reedy Lagoon and Black Swamp in late spring 2017. In the absence of large-bodied carp, aquatic plants flourished and were able to germinate, establish and set seed. In Reedy Lagoon, the managed delivery triggered a dense cover of vulnerable river swamp wallaby-grass. In Black Swamp, the number and distribution of aquatic plants was the highest on record and several plant species not commonly observed were recorded including river swamp wallabygrass and wavy marshwort.
High rainfall in early December 2017 increased flows in the River Murray and delivered minor flows through deeper floodrunners and creeks in upper Gunbower Forest. To maintain the carp exclusions, these flows were prevented from connecting to Reedy Lagoon and Black Swamp. In the absence of large-bodied carp, vegetation in both wetlands proliferated over summer and autumn as water levels receded. A small volume of water remains in both wetlands and is expected to persist in deeper areas to the end of 2017–18.
The improved extent and condition of aquatic vegetation in Reedy Lagoon and Black Swamp provided excellent feeding habitat for many waterbirds, including eastern great egrets and white-faced heron. It also provided breeding habitat for Australasian grebes, white-bellied sea eagles and black swans.
The success of environmental watering in Reedy Lagoon and Black Swamp highlights the benefits of coordinating deliveries of water for the environment with other management actions to maximise environmental outcomes. Carp exclusion plots, established by the Living Murray Intervention Monitoring Program in 2014–15, were again monitored in a few of the forest wetlands. These trial plots demonstrate how floodplain vegetation responds at different stages of their wetting and drying cycles in the absence of large-bodied fish (including carp) as well as grazing by waterbirds and marsupials. Plots that excluded carp, waterbirds and kangaroos had more-abundant and morediverse vegetation than plots that only excluded one species.
In 2017–18, flows in Gunbower Creek allowed large-bodied fish, especially Murray cod, to migrate, spawn, feed and breed. Since implementing managed environmental flows in Gunbower Creek in 2011, the native fish population has steadily increased. Higher flows provided in winter/spring 2017 helped maintain fish nursery habitats, and Gunbower Creek now supports a healthy population of Murray cod of varying ages and greater numbers of golden perch, silver perch and freshwater catfish.
In mid-June 2018, water for the environment was delivered to Gunbower Forest to support river red gums and the flood-dependent understory. The water delivery was timed to maximise deliveries into the forest before irrigation orders (due to resume from 15 August) were to take up much of the capacity of Gunbower Creek. The delivery of environmental water to Gunbower Forest is planned to continue during winter/spring 2018–19.
