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The Thomson River flows from the slopes of the mountains of the Baw Baw Plateau to join the Latrobe River south of Sale. The major tributaries of the Thomson River are the Aberfeldy, Jordan and Macalister rivers, with most unregulated flows originating from the Aberfeldy River.

Environmental water in the Thomson system is held in Thomson Reservoir. A new environmental entitlement in the Thomson system which will provide an additional 3.9 percent of Thomson Reservoir inflows per year will become available for the first time in 2017–18. This extra environmental water will help meet more of the environmental flow objectives for the Thomson River and will provide benefits to native fish including Australian grayling, tupong and Australian bass.

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, relatively intact native riparian vegetation, high-quality instream habitat and low abundance of exotic fish species.

At Cowwarr Weir, the Thomson River splits in two and water can move down the old Thomson River course (reach 4a) and Rainbow Creek (reach 4b). The preference is to pass environmental water down the old Thomson River course to enable fish migration, as Cowwarr Weir prevents migration through Rainbow Creek. The passing flows are split two-thirds down reach 4a and one-third down 4b throughout the year to avoid impacts on Rainbow Creek irrigation customers.

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 values

The Thomson River supports seven species of migratory fish that need to move between the sea and freshwater environments during parts of their life cycle. The threatened Australian grayling is the most significant of these species and is one of the species targeted with environmental flows in the Thomson River. Australian grayling spawn in response to autumn high flows, and the eggs and juveniles spend time at sea before returning to the freshwater reaches of coastal rivers.

The composition and condition of riparian vegetation varies throughout the Thomson River catchment. The vegetation is intact and near-natural upstream of Thomson Reservoir in the Baw Baw National Park. Between Thomson Reservoir and Cowwarr Weir it is mostly in good condition but is moderately infested with blackberry and gorse. Downstream of the Cowwarr Weir, the vegetation is degraded due to stock access and widespread weed invasion.

Social, cultural and economic values

Thomson Reservoir is the largest storage in Melbourne's water supply system and also supplies water to irrigators and towns in Gippsland.

The Thomson River is highly valued for recreation downstream of the Thomson Reservoir to upstream of Cowwarr Weir. The area is popular for camping, kayaking and canoeing. Avid kayakers, canoeists and outdoor recreation operators often take advantage of the whitewater conditions provided with environmental water releases in the upper reaches of the Thomson River.

Waterways in the Thomson system including the Thomson River continue to hold significance for Traditional Owners. Rivers and wetlands in the region contain important ceremonial places and for thousands of years the Thomson River has provided resources such as food and materials to Traditional Owner groups (such as the Gunaikurnai people).

Environmental watering objectives in the Thomson River

Fish icon
Protect and increase populations of native fish, specifically Australian grayling, by providing pool habitat and flows for fish to move upstream and downstream, and to cue spawning
Landscape icon
Scour silt build-up in the river bed to improve the quality of in-stream habitat for aquatic plants and animals
Plant icon
Increase recruitment and growth of native riparian vegetation

Conditions mid-2017

Climatic conditions have varied significantly over the last two years. The 2015–16 water year had below-average rainfall and was very dry. The 2016–17 water year had average to above-average rainfall throughout the winter and spring and below-average rainfall in summer and autumn. These conditions contributed to high and frequent irrigation demands during summer for the last two years.

Environmental water releases in recent years have focussed on providing autumn and spring freshes for spawning and recruitment opportunities for native fish species including Australian grayling, tupong and Australian bass. Low flows have also been provided to enable fish to move between habitats along the river. Wet conditions in winter and spring 2016 meant some of the planned environmental water deliveries were not needed because the objectives were met by unregulated flows. Two spring freshes, two winter freshes and one bankfull event were provided via unregulated flows in 2016–17.

An autumn fresh was provided in 2016 with a reduced magnitude (600 ML/day peak flow rather than 800 ML/ day) to test whether Australian grayling would spawn at a lower flow. Monitoring during the event detected very little spawning and therefore the autumn fresh in autumn 2017 and the planned fresh for autumn 2018 will deliver peaks of 800 ML/day, which is known to trigger Australian grayling spawning behaviour.

Scope of environmental watering

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

Potential environmental watering

Environmental objectives

Spring freshes (1–2 freshes of 800 ML/ day for 4 days each in September–October)

  • Encourage recruitment of juvenile migratory fish species from the estuary
    and ocean

Spring low flows (230 ML/day from October–November)

  • Provide improved passage along the river to enable localised fish movement between habitats

Autumn freshes (1–2 freshes of 800 ML/day for 4 days each in April–May)

  • Provide a downstream migration and spawning cue for migratory fish species including Australian grayling

Autumn/winter low flows (230 ML/day from May– June)

  • Provide improved passage along the river to enable localised fish movement between habitats

Winter freshes (up to 4 freshes of 800 ML/day for 4 days in June–August)

  • Provide a migration and spawning cue for migratory fish species including tupong and Australian bass
  • Maintain/increase riparian vegetation
Summer/autumn freshes (up to 7 freshes of 230 ML/day for 4 days in December–April)
  • Maintain/enhance the native fish community structure by providing habitat
  • Maintain/increase submerged aquatic vegetation
  • Scour sediment exposing fresh habitat areas
  • Maintain/enhance habitat for waterbugs

Risk management

In preparing its seasonal watering proposal, West Gippsland CMA considered and assessed the risks of environmental watering and identified mitigation strategies. Program partners continually reassess risks and mitigation actions throughout the water year.


Waterway managers meet communities on environmental watering regionally, although other program partners also play a role.

In each region of Victoria, community engagement on environmental watering happens when environmental watering objectives and priorities are scoped (long term and annually), when delivering environmental water, and when reporting on environmental watering results.

In the West Gippsland region communities are involved in decisions about the Thomson and Macalister river systems and the Lower Latrobe wetlands. The community is engaged informally and through the Macalister river Project Advisory Group.

Who is engaged and how

Recreational users

A representative of VRFish sits on the Macalister river Project Advisory Group.

West Gippsland Catchment Management Authority engages with Field & Game Australia when developing the Lower Latrobe wetlands seasonal watering proposal (annual scoping). Field & Game Australia shares wetland bird count data with the Catchment Management Authority which helps with reporting on environmental watering outcomes.

The Catchment Management Authority notifies many recreational user groups about environmental water deliveries. These groups include canoe clubs, outdoor education companies and school groups (many of whom come from outside of the region). These groups are interested in managing safety and also achieving opportunities for shared benefits from environmental watering (e.g. kayaking on higher flows in the Thomson river).

Environment groups

Representatives from environment groups (Environment Victoria, Landcare and Native Fish Australia) sit on the Macalister river Project Advisory Group.


Irrigation representatives sit on the Macalister river Macalister river Project Advisory Group.

Southern Rural Water sends environmental water delivery notifications to their irrigation customers on behalf of the Catchment Management Authority. These irrigation customers are often primarily interested in environmental watering from a safety and infrastructure protection perspective.

Traditional owners

Through the Catchment Management Authority Indigenous facilitator, the Gunaikurnai Land and Waters Aboriginal Corporation has been invited to join the Macalister river Project Advisory Group.

The Catchment Management Authority and Gunaikurnai Land and Waters Aboriginal Corporation have a Memorandum of Understanding. The Catchment Management Authority recognises the recently developed Gunaikurnai Land and Waters Aboriginal Corporation draft Whole Of Country Plan which contains aspirations for rivers and wetlands in Gippsland.


The Wellington Shire Council is a member of the Macalister river Macalister river Project Advisory Group.

The Wellington Shire Council, the Latrobe City Council and the Baw Baw Shire Council are all on the Southern Rural Water environmental water delivery notification list.

General public

Public signage informing the general public about upcoming environmental water deliveries is set up a few days before a planned delivery along key recreational sites in the upper Thomson River. This is for primarily for public safety purposes.