VEWH - Lower Latrobe wetlands

The lower Latrobe wetlands (Dowd Morass, Heart Morass and Sale Common) are an important component of the internationally recognised Gippsland Lakes Ramsar site and provide habitat for a variety of waterbirds of state, national and international conservation significance. The wetlands are located on the floodplain of the Latrobe River between its confluence with the Thomson River, and they form part of the Gippsland Lakes system.

River regulation and water extraction from the Latrobe, Thomson and Macalister rivers has reduced the frequency of small and medium-sized floods that naturally wet the lower Latrobe wetlands. Construction of levees and drains and filling of natural depressions have also altered water movement into and through the wetlands. The drainage and flooding regime in all three wetlands is now managed to some extent with regulators connected to the Latrobe River.

System map

Latrobe River and Wetland 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 lower Latrobe wetlands

Maintain the abundance of frog populations

Maintain the abundance of freshwater turtle populations

Maintain or restore a self-sustaining variety of submerged and emergent aquatic vegetation types. Maintain or restore the diversity, condition and/or extent of native riparian vegetation fringing wetlands. Discourage the introduction and spread, or reduce the extent and density, of undesirable/ invasive plants (Sale Common).

Maintain or enhance waterbird breeding, recruitment, foraging and sheltering opportunities

Provide suitable physio-chemical conditions to support aquatic life

Environmental values

Sale Common is one of only two remaining freshwater wetlands in the Gippsland Lakes system, and it provides sheltered feeding, breeding and resting habitat for a large range of waterbirds.

Dowd Morass is a large, brackish wetland that regularly supports rookeries of colonial nesting waterbirds including Australian white ibis, straw-necked ibis, little black and little pied cormorants, royal spoonbills and great egrets.

Heart Morass is also a large brackish wetland, with open expanses providing shallow feeding habitat for waterbirds including black swans, Eurasian coots and a variety of ducks.

Together, the lower Latrobe wetlands function as a diverse and complementary ecological system. Colonial waterbirds breed among swamp paperbark trees at Dowd Morass in spring. Migratory shorebirds feed on the mudflats that are exposed as the wetlands draw down and dry over summer. Waterfowl and fish-eating birds use open-water habitat at the wetlands year-round. The wetlands also support threatened vegetation communities including swamp scrub, brackish herbland and aquatic herbland.

Recent conditions

Climatic conditions in West Gippsland were warmer and drier than average during the 2018–19 water year. Several storms in November 2018 had high rainfall, but none of these delivered significant inflows to the wetlands. Managed water delivery through regulators provided the only inflows to the wetlands in 2018–19.

The regulator to Dowd Morass was opened from August to October 2018, briefly in December 2018 and again in April 2019. The regulator was opened when the Latrobe River was high, to dilute saline water in Dowd Morass.

Heart Morass was partially filled between August and October 2018, and further top-ups were provided in December 2018 and March 2019 to manage acid sulphate soils. The managed inflows reduced salinity in the wetland and inundated the semi-aquatic grasses, which provided food for waterbirds.

Water was allowed to draw down naturally in Heart Morass and Dowd Morass from the middle of summer.

Sale Common received water for the environment throughout winter and spring and was one-third full in October 2018. Large stands of semi-aquatic wetland vegetation (such as knotweed and club-rush) dominated the wetland over summer. By autumn, the semi-aquatic vegetation began to dry out and was replaced by terrestrial grasses and sedges.

The environmental flow recommendations for the Latrobe River, Latrobe River estuary and lower Latrobe wetlands were reviewed and updated in early 2019. The updated recommendations take a more integrated approach to managing all the major waterways in the Latrobe system, and they have informed planning for 2019–20.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the lower Latrobe wetlands

Potential environmental watering action	Functional watering objectives	Environmental objectives
Sale Common
Partial fill (during July to December)	Provide seasonal variation in water depth to support the growth and flowering of semi-aquatic plants Provide appropriate wetland fringing habitat Provide conditions that support waterbug communities and food resources for waterbirds Stimulate bird breeding by providing nesting habitat via wetting reed beds and deep water next to reedbeds
Fill (during August to November)	Wet the outer boundaries of the wetland to support the growth and flowering of riparian and fringing wetland plants Provide connectivity between the river and wetlands
Fill (any time)	Prolong wetted habitat to discourage invasive plants, particularly the excessive spread of giant rush: this is most likely to occur in December and January, but it can happen any time
Partial or near-complete drawdown (during December to April)	Oxygenate the soil for the germination and recruitment of aquatic vegetation Fluctuate water levels to provide conditions for the reproduction and expansion of swamp scrub and tall marsh Allow the die-off of aquatic vegetation and the breakdown of organic matter, to support nutrient recycling Discourage invasive aquatic plants Expose the mudflats and wetland fringe, to increase food sources and foraging opportunities for waterbirds
Fill or partial fill (any time)	Manage unexpected or out-of-season events, which may lead to catastrophic conditions. Such examples are to: - Manage any sudden decline in dissolved oxygen - Provide habitat for waterbirds after breeding events Maintain ecosystem resilience
Dowd Morass
Fill or partial fill (any time)	Minimise the risk of salt water inundation Manage unexpected or out-of-season events which may lead to catastrophic conditions. Such examples are to: - Respond to suddenly increasing salinity following intrusions/high water levels from Lake Wellington - Manage any sudden decline in dissolved oxygen and pH - Provide habitat for waterbirds after breeding events Maintain ecosystem resilience
Partial fill (during March to December)	Maintain or improve water quality by reducing salinity Provide seasonal variation in water depth, to support the growth and flowering of semi-aquatic plants Provide appropriate wetland fringing habitat and allow the growth and reproduction of waterbug communities Flood the banks and riparian zone, to create conditions to support bird-nesting Provide connectivity between the river and wetlands and between wetlands Provide conditions that support waterbug communities and food resources for waterbirds Stimulate bird breeding by providing nesting habitat via inundating reed beds and deep water next to reedbeds
Fill (during August to November)	Wet vegetation that provides habitat for waterbirds (e.g. floodplain riparian woodland) Provide conditions that support waterbug communities and food resources for waterbirds Stimulate bird breeding by providing nesting habitat via inundating reed beds and deep water next to reedbeds Flood the banks and riparian zone to create conditions for waterbird nesting Provide connectivity between the river and wetlands and between wetlands
Partial or near-complete drawdown (during January to March)	Oxygenate the soil for the germination and recruitment of aquatic vegetation Fluctuate water levels to provide conditions for the reproduction and expansion of swamp scrub and tall marsh Allow the die-off of aquatic vegetation and the breakdown of organic matter, to encourage nutrient recycling Expose the mudflats and wetland fringe to increase food sources and foraging opportunities for waterbirds
Heart Morass
Fill or partial fill (any time)	Keep soils wet to minimise the risk of acid sulfate soils Manage unexpected or out-of-season events, which may lead to catastrophic conditions. Such examples are to: - Respond to decreasing pH from the rewetting of exposed acid sulfate soils (most likely during high-wind events) - Respond to suddenly increasing salinity following intrusions/high water levels from Lake Wellington - Provide habitat for waterbirds following bird-breeding events Maintain ecosystem resilience
Partial fill (during August to December)	Provide seasonal variation in water depth to support the growth and flowering of semi-aquatic plants Provide appropriate wetland fringing habitat Provide conditions that support waterbug communities and food resources for waterbirds Stimulate bird breeding by providing nesting habitat via inundating reed beds and deep water next to reedbeds
Flushing flow (during June to November)	Reduce salinity levels by exporting salts and sulfates from the wetland, helping to maintain vegetation diversity Disperse seeds and propagules
Drawdown (during December to February)	Increase soil oxygenation for the germination and recruitment of aquatic vegetation Fluctuate water levels to provide conditions for the reproduction and expansion of swamp scrub and tall marsh Allow the die-off of aquatic vegetation and the breakdown of organic matter, encouraging nutrient recycling Expose the mudflats and wetland fringe, to increase food sources and foraging opportunities for waterbirds