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Thomson Reservoir harvests most of the flow from the Thomson River upper catchment and has a significant effect on flow in all downstream reaches. Natural flow from the Aberfeldy River, which meets the Thomson River below Thomson Reservoir, is essential for providing natural freshes and high flows in the Thomson River.

Water for the environment is held in the Thomson Reservoir and released into the river as required. Reach 3 of the Thomson River (from the Aberfeldy River confluence to Cowwarr Weir) is the highest priority for environmental watering due to its heritage river status, high-value native streamside vegetation, high-quality in-stream habitat and low abundance of exotic fish species.

At Cowwarr Weir, the Thomson River splits into the old Thomson River course (reach 4a) and Rainbow Creek (reach 4b) (see system map). Passing flows throughout the year are split two-thirds down reach 4a and one-third down 4b to avoid impacts to irrigators located on Rainbow Creek. Water for the environment is primarily delivered to the old Thomson River course (reach 4a) to support fish migration, because Cowwarr Weir impedes fish movement through Rainbow Creek.

The Heyfield wetlands is a cluster of several pools located between the Thomson River and the township of Heyfield. Due to the construction of levees and weirs along the Thomson River, natural wetting of river waters to the wetland rarely occurs; and while the largest pool receives stormwater from the Heyfield township, smaller ponds rely on rainfall or pumped water for the environment to maintain environmental values. These values include significant revegetation that has been done in recent years.

Traditional Owners
Storage manager
Environmental water holder

System map

Thomson 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 Thomson River

Restore populations of native fish, specifically Australian grayling

Maintain/enhance the structure of native fish communities

Reduce competition from exotic fish
Frog icon
Maintain the existing frog population and enhance opportunities for breeding
Landscape icon
Maintain channel form diversity including pools, to provide a variety of habitats for aquatic animals
Platypus icon
Increase the abundance of platypus
Plant icon
Maintain and restore the structural diversity and zonation of streamside vegetation and reduce terrestrial encroachment/invasion (Thomson River)

Increase the recruitment and growth of native in-stream, fringing and streamside vegetation (Thomson River)

Maintain the existing vegetation, promote the growth and establishment of semi-aquatic species (Heyfield wetlands)

Enhance the resilience of semi-aquatic and streamside woodland species (Heyfield wetlands)
Insect icon
Restore and maintain the natural invertebrate community
bird icon
Provide freshwater habitat for migratory and non-migratory wetland birds within the Gippsland Plains landscape

Continue to support observed terrestrial woodland and grassland birds by maintaining their streamside woodland habitat

Environmental values

The Thomson River supports six native species of migratory fish  that need to move between the sea and freshwater environments to complete their life cycles. A focus for environmental flows management is the Australian grayling, which is listed as a threatened species in Victoria. Australian grayling spawn in response to autumn freshes, and the larvae and juveniles spend time at sea before returning to the freshwater sections of coastal rivers.

The composition and condition of streamside vegetation varies throughout the Thomson River catchment. The  vegetation is intact and near-natural condition above Thomson Reservoir in the Baw Baw National Park. Streamside vegetation between Thomson Reservoir and Cowwarr Weir is mostly in good condition but is affected by exotic weeds including blackberry and gorse. Below the Cowwarr Weir, the vegetation is degraded due to stock access and widespread weed invasion.

The Heyfield wetlands are one of the few remaining freshwater wetland sites in the Gippsland Plains landscape area, and they are a source of habitat for aquatic and terrestrial animals that prefer shallow, slow-moving waterbodies, including threatened migratory birds.

Traditional Owner cultural values and uses

The Gunaikurnai have had a continued connection to Gunaikurnai Country for thousands of years, including with the waterways in the Latrobe River system (which the Thomson River feeds into). For the Gunaikurnai as traditional custodians there are immense challenges to heal, protect and manage Country which has been drastically altered since colonisation. Gunaikurnai see all of Country as connected with no separation between landscapes, waterways, coasts and oceans and natural and cultural resources – the cultural landscape is interdependent.

Gunaikurnai Land and Waters Aboriginal Corporation (GLaWAC) are working with the West Gippsland CMA to determine how to express Gunaikurnai objectives for water in a way that contributes to seasonal watering proposals from the perspective of traditional custodians, with traditional knowledge.

Traditionally, Carran Carran (Thomson River) was an important meeting place and a place to camp. Today, the majority of Carran Carran is inaccessible to the Gunaikurnai making it difficult to meet and yarn along the river. Assessments for watering requirements of Carran Carran for the Gunaikurnai have been based on cultural indicators, including:

  • the condition of the lower Latrobe wetlands (which Carran Carran helps supply)
  • the condition and prevalence of plants and animals with cultural values and uses
  • species known to be indicators of water quality, water regimes and Healthy Country.

GLaWAC shared with the West Gippsland CMA plant and animal species of cultural significance in and around the waterways of the Latrobe Valley, and the importance of specific watering decisions to support them.

Watering requirements to support cultural values and uses include:

  • timing of environmental watering planned in partnership with GLaWAC to support a seasonal flow regime and wet and dry periods that embody Healthy Country
  • maintaining freshwater supply to Latrobe estuary, Dowd Morass, Sale Common and Heart Morass and associated freshwater habitats. The lower Latrobe wetlands are an important resource for the Gunaikurnai
  • providing connectivity between reaches and onto floodplains to support dependent plants and animals with cultural values and uses of significance to the Gunaikurnai
  • maintaining water quality to support health of native plants and animals with cultural values and uses of significance to the Gunaikurnai.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 1, West Gippsland CMA considered how environmental flows could support values and uses including:

  • water-based recreation (such as kayaking, canoeing, fishing and swimming)
  • riverside recreation and amenity (such as camping, hiking, duck hunting and birdwatching)
  • community events and tourism (such as community education and events at the Heyfield wetlands, and visitation by locals and non-locals)
  • socio-economic benefits (such as outdoor education companies).

If the timing or management of planned environmental flows may be modified to align with a community benefit, this is acknowledged in Table 1 with an icon.

Kayak icons

Watering planned to support water sports activities (e.g. canoeing, kayaking, rowing, swimming, water skiing)

Camping icon

Watering planned to support peaks in visitation (e.g. camping or other public activities on long weekends or school holidays)

Autumn, winter and spring freshes create ideal whitewater rafting conditions for kayakers and canoers in the Thomson River. The timing of environmental flows may be adjusted to optimise opportunities to support these recreation activities, where it does not compromise environmental outcomes. Recreational kayakers and outdoor companies can take advantage of the whitewater rafting conditions as a result of these freshes.

For example, the spring fresh, which aims to cue the migration of Australian grayling, may be delivered over the Melbourne Cup racing carnival weekend in November when many people take advantage of the Tuesday public holiday to spend a long weekend kayaking on the Thomson River.  Recreational users interested in this shared benefit can register on the West Gippsland CMA website to receive a notification of the upcoming watering event.

Recent conditions

The start of the 2019–20 water year was warmer and rier than average in the Thomson River catchment, but above-average rainfall over summer increased inflows to the Thomson Reservoir and boosted water availability. Thomson Reservoir did not spill, so moderate releases were made throughout the year to supply minimum passing flow requirements, to meet irrigation demand and for environmental watering. Environmental watering actions were delivered in line with dry conditions during the first half of the year and average conditions from late summer.

Other than bankfull and overbank flows (which cannot be managed with water for the environment), all recommended environmental flows for the Thomson River were achieved through natural flows, managed environmental flows, operational deliveries or a combination of these.

Water for the environment was used to meet high-priority freshes in spring and autumn and to maintain target low flows as needed. The spring and autumn freshes are particularly important to cue native fish to move between habitats, supporting their breeding and recruitment. Water for the environment was delivered to Heyfield wetlands in August and October 2019 to enhance the growth of recently planted aquatic and streamside

Scope of environmental watering

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

Potential environmental watering action

Functional watering objectives

Environmental objectives

Thomson River

Autumn fresh (two freshes of 800 ML/day for seven days during April to May)

  • Trigger the downstream migration (and spawning) of Australian grayling (April)
  • Trigger the downstream migration of tupong and Australian bass (May)
  • Carry plant seeds from the upper catchment for deposition downstream
  • Deposit sediments on benches, to provide substrate for vegetation
  • Wet the bank/bench to deliver dissolved and/or fine particulate organic matter
  • Scour substrates to remove accumulated fine sediment

Fish iconMountain iconsPlant iconInsect icon

Spring fresh (one to two freshes of 800 ML/day for seven days during September to November)

Camping iconKayak icons

  • Trigger upstream fish migration from marine/estuarine habitats and the recruitment of juvenile native species including Australian grayling and Australian bass (October to November)
  • Improve and maintain streamside vegetation by inundating the benches and providing variable water levels for plant zonation
  • Carry plant seeds from the upper catchment for deposition downstream
  • Deposit fine particulate sediments on the benches
  • Scour substrates to remove accumulated fine sediment

Fish iconMountain iconsPlant icon

Summer/autumn fresh (two freshes1 of 230–350 ML/ day for seven days during December to March)

  • Increase the water depth to provide habitat for native fish
  • Wet aquatic and fringing vegetation to maintain its condition and support its growth
  • Maintain the physical form and functioning of the channel through mobilisation of fine sediments

Fish iconMountain iconsPlant icon

Autumn/winter/spring low flow (125–350 ML/day during May to November)2

  • Increase the available habitat for waterbugs
  • Regulate the water temperature and wet large woody debris to provide food and shelter for waterbugs and fish
  • Increase the water depth to facilitate platypus and fish movement between localised habitats and increase foraging opportunities
  • Wet low-lying benches to prevent encroachment by invasive plants and permit seed dispersal

Fish iconMountain iconsPlant iconInsect icon

Summer/autumn low flow (340 ML/day at reach 6 during December to May)

  • Partially flush the upper water column in the Thomson estuary, helping to sustain waterbug communities and fish by maintaining oxygen levels
  • Prevent high salinity levels, helping to maintain emergent macrophyte vegetation
  • Provide freshwater to the Latrobe River system

Fish iconMountain iconsPlant iconInsect icon

Heyfield wetlands

Fill (in August)

  • Wet ponds to capacity, to stabilise the banks and support the spring growth of semi-aquatic vegetation
  • Provide freshwater habitat for waterbirds and frogs (such as growling grass frogs and golden bell frogs)

Frog iconPlant iconHeron icon

Top-ups to maintain water level, as required (during October to November)

  • Top up ponds before summer to maintain the existing vegetation and enhance its recruitment by triggering seed dispersal
  • Provide freshwater habitat for waterbirds and frogs (such as growling grass frogs and golden bell frogs)

Frog iconPlant iconHeron icon

Partial drying (during December to February)

  • Oxygenate surface soils, break down accumulated organic matter and cycle nutrients
  • Enhance waterbird food availability by exposing the mudflats and provide access to burrowing invertebrates

Frog iconPlant iconHeron icon

1 Additional summer freshes are likely to be met with operational water releases.

2 Passing flows may be flexibly managed at rates less than 230 ML per day in July.


Table 2 shows the partners with which West Gippsland CMA engaged when preparing the Thomson 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 Latrobe system seasonal watering proposal

Partner and stakeholder engagement
  • Heyfield Wetlands Committee
  • Cowwarr Landcare Group
  • Waterwatch volunteers
  • Landcare groups
  • Birdlife Australia
  • Melbourne Water
  • Southern Rural Water
  • Gippsland Water
  • Department of Environment, Land, Water and Planning - Water and Catchments
  • Individual landholders
  • Tourism operators
  • VRFish
  • Arthur Rylah Institute (Department of Environment, Land, Water and Planning)
  • Gunaikurnai Land and Waters Aboriginal Corporation

Page last updated: 22/01/21