Macalister River

The Macalister River flows from Mt Howitt in the Alpine National Park and joins the Thomson River south of Maffra. The river winds its way in a south-easterly direction through mostly forested, confined valleys and narrow floodplains upstream of Lake Glenmaggie. The downstream reaches flow through wide alluvial floodplains that have been cleared for agriculture. The Wellington River and Glenmaggie Creek are the main tributaries of the Macalister River.

Lake Glenmaggie is the major water-harvesting storage regulating the Macalister River. Maffra Weir is a small diversion weir located further downstream in Maffra.

Before the construction of Lake Glenmaggie, the Macalister River would regularly receive high and medium flows in winter and spring. Although Lake Glenmaggie regularly spills, high flows are less frequent than natural because much of the water is captured by the storage. A notable impact of irrigation and water-harvesting is reversed seasonality of flows between Lake Glenmaggie and Maffra Weir. Summer flows through this reach are much higher than natural due to the delivery of irrigation water. Winter flows in this reach are lower than natural because a high proportion of the inflows are captured and there are no irrigation demands over winter. Downstream of Maffra Weir, most flows are diverted for irrigation in summer/autumn. The changed hydrology restricts fish migration, limits the growth and recruitment of in-stream and riparian plants and reduces the quality of in-stream habitat.

Water for the environment is stored in Lake Glenmaggie and released to the Macalister River. The river is divided into two reaches for the purposes of managing environmental flows: Lake Glenmaggie to Maffra Weir (reach 1) and Maffra Weir to the Thomson River (reach 2).

Maffra Weir is a major barrier to fish movement along the river, so environmental watering for migratory fish objectives mainly focus on reach 2. All other objectives apply to both reaches 1 and 2.

System map

Macalister System — Grey river reaches have been included for context. The numbered reaches indicate where relevant environmental flow studies have been undertaken. Coloured reaches can receive environmental water.

Environmental watering objectives in the Macalister River

Increase the distribution, recruitment and abundance of all native fish, and increase opportunities for the spawning and recruitment of native migratory fish (such as the Australian grayling)

Improve and maintain the form of the riverbank and bed to provide physical habitat for aquatic ecology

Increase the abundance of platypus and rakali (water rats)

Improve native emergent (non-woody) and fringing (woody) vegetation in the riparian zone.  

Reinstate or instate submerged aquatic vegetation.

Increase the abundance and number of functional groups of waterbugs

Environmental values

There are seven migratory native fish species that move between the Macalister River, the estuary and the sea to complete their life cycle. These species include the Australian grayling, short-finned eel, long-finned eel, tupong, Australian bass, short-headed lamprey and common galaxias. Yellow-eye mullet, which is an estuarine species, has been recorded in the river. Platypus and rakali (water rats) are widely distributed through the Macalister River and its tributaries.

The riparian vegetation corridor along the regulated reaches of the Macalister River is fragmented. Immediately downstream of Lake Glenmaggie, the vegetation is in good condition and includes remnant river red gums and good-quality stands of shrubs, particularly in areas where revegetation has occurred in combination with stock exclusion. Further downstream, the vegetation is degraded. In recent years, the cover of in-stream vegetation has declined, which may be due to a combination of increased water turbidity, erosion and a lack of an appropriate water regime to encourage plant growth. The cover of non-woody plants (such as reeds, sedges and rushes) along the fringes of the river is patchy.

Recent conditions

Climatic conditions in the Macalister River catchment have been very dry over the last two years.

The 2017–18 year began with a dry winter/spring. Average rainfall in December 2017 and January 2018 caused Lake Glenmaggie to spill in December 2017, but the rest of summer/autumn 2018 were drier than average.

Dry conditions persisted into 2018–19, with belowaverage to well-below-average rainfall and above-average temperatures for most of the year. Lake Glenmaggie did not spill in 2018–19, which is rare for this system.

The reach between Lake Glenmaggie and Maffra Weir had consistent flow to meet operational demands throughout the irrigation season. Due to low inflows however, passing flows at Maffra Weir were reduced in March from 60 ML per day to 30 ML per day or less, in accordance with system rules.

Water for the environment was used to supplement low passing flows in reach 2 from late March to protect water quality, and it was also used to provide freshes at critical times and to supplement low flows when irrigation demand fell.

A winter fresh was delivered in August 2018 to trigger the migration and spawning of tupong and Australian bass. A spring fresh was delivered in early November 2018 to encourage juvenile fish to migrate into the Macalister River from the sea, and to wet bankside vegetation and enable native seed dispersal.

An autumn fresh targeting fish migration was not delivered in April 2019. This fresh is usually timed to coincide with releases in the Thomson and Latrobe rivers to enhance migration cues. Construction of the Thomson River fishway at Horseshoe Bend meant an autumn fresh could not be delivered in the Thomson River. The lack of a complementary flow in the Thomson River reduced the value of the fresh in the Macalister River, and it was decided that the water should be held in storage to meet anticipated environmental demand in 2019–20. Foregoing the autumn fresh for one year is not expected to affect Australian grayling populations, but delivering the event in autumn 2020 will be a priority.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the Macalister system

Potential environmental watering action	Functional watering objectives	Environmental objective
*Macalister River reaches 1 and 2*
Winter to summer low flow (up to 90 ML/day during June to December)	Provide hydraulic habitat for fish by increasing the water depth in pools Provide fish passage for local movement through minimum depth over riffles Provide permanent wetted habitat for waterbugs through minimum water depth in pools Provide connectivity throughout the river for the local movement of platypus and raali (water rats), as well as protection from predation, access to food sources; and to maintain refuge habitats Provide flows with low water velocity and appropriate depth to improve water clarity and enable establishment of in-stream vegetation Provide sustained wetting of low-level benches (increasing water depth) to limit terrestrial vegetation encroachment
Summer/autumn low flow (35–90 ML/day during January to May)	Maintain the water depth in pools and hydraulic habitat for native fish Maintain permanent wetted habitat in pools and riffles for waterbugs Maintain shallow, slow-flowing habitat to enable the establishment of in-stream vegetation Maintain a minimum depth in pools to allow for turnover of water and to slow degradation of water quality to support aquatic life Expose and dry lower channel features for re-oxygenation
Spring fresh (up to 1,500 ML/day for three days during September to October)	Cue the up-stream migration of adult fish (e.g. short-headed lamprey), and the recruitment of juveniles (e.g. Australian grayling, tupong, common galaxias, Australian bass, short and long-finned eels) from marine/estuarine environments Wet a greater area of the stream channel (increasing water depth) to limit terrestrial vegetation encroachment Wet mid and higher-level benches to water woody vegetation Flush pools to improve the water quality and increase wetted habitat for waterbugs Provide flows with sufficient shear stress to flush fine sediment from small gaps to improve geomorphic habitat
*Macalister River reach 2*
Autumn fresh (up to 350 ML/day for four to five days during April to May)	Cue downstream migration for Australian grayling towards the estuary for spawning
Spring/summer fresh (700 ML/day for up to five days during September to December)	Cue upstream migration of adult fish (e.g. short-headed lamprey), and recruitment of juveniles (e.g. Australian grayling, tupong, common galaxias, Australian bass, short and long-finned eels) from marine/ estuarine environments Wet a greater area of the stream channel (increasing water depth) to limit terrestrial vegetation encroachment Wet low and mid-level benches to facilitate the dispersal of emergent and fringing vegetation throughout the reach
Summer/autumn fresh (one to three freshes of 140 ML/day for three days during December to May)	Increase the depth to allow fish to move throughout the reach Flush pools to maintain water quality Flush substrates and improve the quality of existing waterbug habitat and food supply Wet low benches to facilitate the longitudinal dispersal of emergent vegetation Provide flows with sufficient shear stress to flush fine sediment from small gaps to improve geomorphic habitat
Winter fresh (one to two freshes of 700 ML/day for four to five days during June to August)	Cue the downstream migration of tupong and Australian bass towards the estuary for spawning (Australian bass) and breeding (tupong)

Engagement

Table 2 shows the partners and stakeholder organisations with which West Gippsland CMA engaged when preparing the Macalister system seasonal watering proposal.

Seasonal watering proposals are informed by longer-term regional catchment strategies, regional waterway strategies, environmental flow studies, water management plans and other studies. These incorporate a range of environmental, cultural, social and economic perspectives and longerterm integrated catchment and waterway management objectives. For further details, refer to the West Gippsland Regional Catchment Strategy and West Gippsland Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Macalister system seasonal watering proposal

Partner and stakeholder engagement
Environment Victoria Maffra & Districts Landcare Network Native Fish Australia Arthur Rylah Institute Gippsland Water Macalister Irrigation District irrigators and diverters Wellington Shire Council Southern Rural Water Victorian Environmental Water Holder VRFish Local birdwatchers Kayakers and canoers Gunaikurnai Land and Waters Aboriginal Corporation

Page last updated: 12/12/19