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Lindsay, Mulcra and Wallpolla islands cover over 26,100 ha of Victorian floodplain in the Murray- Sunset National Park, as Figure 5.2.5 shows. They form part of the Chowilla Floodplain and Lindsay-Wallpolla islands icon site that straddles the Victoria and South Australia border in the mid-Murray river system.

The Lindsay, Mulcra and Wallpolla islands floodplain is characterised by a network of permanent waterways, small creeks and wetlands. The Lindsay River, Potterwalkagee Creek and Wallpolla Creek form the southern boundaries of the site and create large floodplain islands with the River Murray to the north.

In their natural state, these waterways and wetlands would regularly flow and fill in response to high water levels in the River Murray. Large floods still occur, but major storages in the upper reaches of the River Murray system have reduced the frequency of small- to moderate-sized floods.

Flows in the mid-Murray river system are regulated through a series of weir pools, generally referred to as locks. Water levels in the weir pools are managed primarily to provide safe navigation and adequate water levels for off-stream diversion via pumps. In recent years, the water level of weir pools 7 and 8 has also been managed to achieve ecological benefits in the River Murray channel, for example by lowering pool levels to increase the extent of fast-flowing habitat, which is preferred by large-bodied native fish (such as Murray cod).

Weir pool levels have a big effect on flows in Mullaroo Creek, the Lindsay River and Potterwalkagee Creek. When water levels in locks 7 and 8 are raised above the full supply level (FSL), flows to the Lindsay River and Potterwalkagee Creek increase; when weir pools are lowered, flows to both the Lindsay and Potterwalkagee reduce and eventually they stop flowing. Mullaroo Creek is less-affected by weir pool levels, because flows are controlled through the Mullaroo Creek regulator which connects the creek and the River Murray. Moderate lowering of the lock 7 weir pool level has little effect on Mullaroo Creek, but lowering to or beyond 0.5 m below FSL makes it difficult to deliver the recommended minimum flow of 600 ML per day that is required for native fish.

Fluctuation of weir pool levels is a major management consideration for jurisdictions that manage flows in the River Murray and the anabranch waterways of Lindsay, Mulcra and Wallpolla islands. Environmental objectives and associated water regimes for the River Murray sometimes conflict with those for the Lindsay, Mulcra and Wallpolla anabranch systems, so responsible agencies in Victoria and NSW and the Murray-Darling Basin Authority need to collaboratively plan how to manage weir pools and flows effectively.

System map

Environmental watering objectives in Lindsay, Wallpolla and Mulcra

Fish icon
Increase the abundance, diversity and distribution of native fish
bird icon
Increase the waterbird population by providing feeding and breeding habitat in floodplain wetlands
Plant icon
Increase the abundance, diversity and distribution of wetland vegetation

Environmental values

The Lindsay, Mulcra and Wallpolla islands represent three separate anabranch systems including streams, billabongs, large wetlands and swamps. When flooded, waterways and wetlands within these systems provide habitat for native fish, frogs, turtles and waterbirds. Terrestrial animals (such as woodland birds) also benefit from improved productivity and food resources when the system floods. Large floodplain wetlands (such as Lake Wallawalla) can retain water for several years after inundation, and they provide important refuge for wetland-dependent species and support terrestrial animals (such as small mammals and reptiles).

Mullaroo Creek and the Lindsay River support one of the most-significant populations of Murray cod in the lower River Murray. These waterways provide fast-flowing habitat that Murray cod favour, and contrast with the mostly slowflowing and still habitats created by the nearby River Murray weir pools. Mature breeding fish in Mullaroo Creek and Lindsay River produce juveniles that subsequently colonise other parts of the Murray system. Waterways and wetlands throughout the icon site support several other fish species including freshwater catfish, silver perch, Murray-Darling rainbowfish and unspecked hardyhead.

The reduced frequency and duration of floods in the River Murray has degraded the water-dependent vegetation communities throughout the Lindsay, Mulcra and Wallpolla island system, which has in turn reduced the diversity and abundance of animals that rely on healthy vegetation for habitat.

Recent conditions

Flows in the major Victorian and NSW tributaries of the southern Murray-Darling Basin were well-below average for the duration of 2018–19, and there was little to no inflow from the Darling River. As a result, there were no unregulated flows in the mid-Murray system in 2018–19.

The primary focus of environmental watering in the Lindsay, Mulcra and Wallpolla islands anabranch system in 2018–19 was to maintain flowing habitat in Mullaroo Creek, to help native fish survive and recruit. Flows in Mullaroo Creek varied between 400 and 1,200 ML per day throughout the year, with the higher-magnitude flows delivered in spring to support Murray cod.

The weir pool level in lock 8 was at FSL or lower all year round, which prevented any flows in Potterwalkagee Creek. The lock 7 weir pool level was too low for most of the year to provide flows to the upper Lindsay River. The exception was a short period in spring 2018 when the weir pool was raised to 0.3 m above FSL, which provided minor flows of 40 ML per day via the northern inlet. Water for the environment was delivered to Wallpolla Horseshoe, to provide feeding habitat for waterbirds and improve the condition of aquatic vegetation.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for Lindsay, Wallpolla and Mulcra islands

Potential environmental
watering action

Functional watering objective Environmental

Environmental objective

Lindsay Island – Mullaroo Creek

Year-round low flows (minimum of 600 ML/day)

  • Maintain fast-flowing habitat for native fish (such as Murray cod, silver perch and golden perch)
Fish icon 

Spring fresh (one fresh of up to 1,200 ML/day for up to three months during September to November)

  • Initiate fish movement and spawning and improve recruitment opportunities for native fish

Fish icon

Winter/spring/summer high flow (one high flow of more than 1,200 ML/day for a maximum of nine months during July to March)
  • Extend the duration of higher flows to support dispersal, spawning and recruitment opportunities for native fish
Fish icon
Lindsay Island – Lindsay River
Winter/spring fresh (one fresh of up to 270 ML/day via the northern regulator and up to 120 ML/day via the southern regulator for a maximum of four months during August to November)
  • Provide temporary flowing habitat to support dispersal, spawning and recruitment opportunities for native fish
  • Inundate the substrate and debris (snags) to promote the growth of biofilms, which provide a food source for animals higher in the food chain

Fish icon

Winter/spring/summer high flow (one high flow of up to 450 ML/day via the northern regulator and up to 450 ML/day via the southern regulator for a maximum of nine months during July to March)
  • Extend the duration of flowing habitat to support dispersal, spawning
    and recruitment opportunities for native fish

Fish icon

Lindsay Island wetlands
Websters Lagoon (complete fill in spring)
  • Provide connection between Websters Lagoon and the River Murray to allow the exchange of carbon, nutrients and aquatic biota between the wetland and the river
  • Provide conditions for lake bed herbaceous plants to grow in the drawdown phase after watering
  • Provide variable water levels in the littoral zone to provide feeding habitat for shorebirds
  • Provide open-water habitat as refuge and feeding habitat for
    waterbirds

Fish iconPlant iconHeron icon

Mulcra Island – Potterwalkagee Creek
Spring fresh (one fresh of up to 450 ML/day via the Stoney Crossing regulator and up to 370 ML/day via the upper Potterwalkagee Creek regulator for a maximum of 3 months during September to November)
  • Provide temporary flowing habitat to support dispersal, spawning and
    recruitment opportunities for native fish
  • Inundate the substrate and debris (snags) to promote the growth of
    biofilms, which provide a food source for animals higher in the food
    chain

Fish icon

Winter/spring/summer high flow (one high flow of up to 1,000 ML/day via the Stoney Crossing and upper Potterwalkagee Creek regulators for a maximum of nine months during July to March)
  • Extend the duration of flowing habitat to support dispersal, spawning and recruitment opportunities for native fish

Fish icon

Wallpolla Island
Finnigans Creek (complete fill in winter/spring)
  • Provide connection between Wallpolla East, Sandy Creek and Finnigans Creek to allow nutrient exchange, increase wetland productivity and the dispersal of plant propagules
  • Inundate/drown river red gum saplings in the bed of Wallpolla Horseshoe to limit their coverage
  • Provide variable water levels in the littoral zone to improve wetland productivity and promote the growth of native aquatic and fringing plants
  • Provide variable water levels in the littoral zone to provide feeding habitat for shorebirds
  • Provide open-water habitat as refuge and feeding habitat for waterbirds

Plant iconHeron icon

Sandy Creek (complete fill in winter/spring)
Wallpolla East (complete fill in winter/spring)
Wallpolla Horseshoe (partial or complete fill any time)

Engagement

Table 2 shows the partners and stakeholder organisation with which Mallee CMA engaged when preparing the Lindsay, Mulcra and Wallpolla islands 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 Mallee Regional Catchment Strategy and Mallee Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Lindsay, Mulcra and Wallpolla islands seasonal watering proposal

Partner and stakeholder engagement

  • Mallee Tours
  • Mildura Information Centre
  • Murray Offroad Adventures
  • Sunraysia Apiarist Association
  • Visit Mildura
  • Wildside Outdoors
  • Mildura Rural City Council
  • Commonwealth Environmental Water Office
  • Murray-Darling Basin Authority
  • Parks Victoria
  • Victorian Environmental Water Holder
  • Department of Environment, Land, Water and Planning
  • Mildura Birdlife Club
  • Sunraysia Bushwalkers
  • First People of the Millewa-Mallee Aboriginal Corporation

Page last updated: 12/12/19