VEWH - Hattah Lakes

The ecology of the Hattah Lakes and surrounding floodplain is strongly influenced by flooding regimes of the River Murray. The system fills when there are high flows in the River Murray, and some lakes hold water for numerous years after floods recede. Regulation of the River Murray has significantly reduced the frequency and duration of small- to medium-sized natural floods in the Hattah Lakes system. Over time, this has degraded vegetation communities and reduced the diversity and abundance of animals that use the vegetation and wetlands for habitat and food.

The Hattah Lakes complex can be broadly divided into the southern Hattah Lakes, which contain permanent to semi- permanent wetlands, and the higher-elevation northern Hattah Lakes, which are mostly ephemeral wetlands.

The Messenger, Oateys and Cantala regulators allow water to flow between the River Murray and the Hattah Lakes. When flows in the River Murray are about 26,000 ML per day, water begins to flow through the Messenger regulator into Chalka Creek and through to the Hattah Lakes complex. A permanent pump station has also been constructed that can deliver up to 1,000 ML per day to Hattah Lakes through Chalka Creek. The regulators and pump station are used in combination with several small constructed levees to restore a beneficial pattern of flooding to the lakes.

Lake Kramen in the south-east of Hattah-Kulkyne National Park is disconnected from the main Hattah Lakes complex. The Hattah Lakes pump station can deliver up to 145 ML per day to Lake Kramen to restore flooding regimes.

System map

Environmental watering objectives in the Hattah Lakes

Increase the fish population by supporting breeding

Restore and maintain a mosaic of healthy wetland and floodplain plant communities

Provide feeding and nesting habitat for the successful recruitment of waterbirds and woodland birds

Environmental values

Hattah Lakes is home to a diverse range of flood- dependent vegetation that changes with the topography
of the landscape. Vegetation types range from wetland communities in lower-lying areas that require almost annual flooding to lignum and black box communities situated higher on the floodplain that only need flooding once every four to five years on average.

A combination of natural flooding and the delivery of environmental flows since 2010 has improved tree canopy health and recruitment of black box and river red gum communities throughout the Hattah Lakes. Woodland birds (including the endangered regent parrot) have benefitted from the improved tree health.

Hattah Lakes provides important waterbird breeding sites in an arid landscape. A total of 34 species of waterbirds are known to breed at the lakes when conditions are suitable. Another six species of waterbirds breed in the surrounding floodplain. Wetland drought-refuge sites are limited in
the region, making Hattah Lakes critically important for waterbirds and terrestrial animals.

The Hattah Lakes support native fish species (such as golden perch and endangered freshwater catfish), which can move between the lakes and the River Murray when flows are suitable. Fish can also persist in permanent wetlands in the Hattah Lakes during dry years.

Recent conditions

Hattah Lakes last received natural inflows from the River Murray during spring 2016. Over 110 GL of water for the environment was delivered to Hattah Lakes between July and October 2017 via the Hattah pumps station, to build on environmental outcomes from the 2016 floods. Almost half the water pumped to the lakes flowed back into the River Murray, providing environmental benefits to high-priority environmental watering sites downstream.

Environmental flows in 2017 provided the most-extensive floodplain inundation at Hattah Lakes since the 1990s and supported the germination, growth and recovery of black box trees. Over several years, there has also been an increase in wetland plant diversity, demonstrated recruitment of small-bodied fish and an increased abundance of woodland birds.

The 2017–18 and 2018–19 summers were exceptionally hot and dry, and lakes within the Hattah complex completely dried, except Hattah Lake and Mournpall Lake.

This drying pattern is important and has allowed floodplain and wetland plant communities to germinate, grow and reproduce a seedbank in preparation for the next flood.

Lake Kramen was last filled in 2014–15. It did not receive any inflow during the 2016 floods, and it has been completely dry since 2017. The dry phase allowed the growth of lake bed vegetation, which will provide an important source of carbon to support productive foodwebs when the wetland is next filled.

Scope of environmental watering

Potential environmental watering actions and objectives for the Hattah Lakes

Potential environmental watering action¹	Functional watering objective	Environmental objectives
Lake Kramen (fill to 46.0 m AHD in winter/spring)	Inundate fringing river red gums and black box trees to stimulate their growth and improve their condition Provide refuge and feeding habitat for waterbirds Provide conditions for lake bed herbaceous plants to grow in the drawdown phase after watering
Southern Hattah Lakes² (partial fill to 42.5 m AHD in autumn/winter)	Stimulate growth to improve the condition of river red gums Provide refuge and feeding habitat for waterbirds Stimulate the growth of aquatic vegetation in wetlands that are currently dry
Hattah Lakes (floodplain inundation up to 45.0 m AHD at any time if there is a natural flood)	Inundate river red gums and black box on the floodplain to stimulate the growth and improve the condition of mature trees Provide suitable soil conditions for the germination of black box trees on the floodplain and support the growth of trees that germinated in the flows provided in 2017 Provide suitable conditions to support waterbird and woodland bird breeding and feeding Provide connections to allow native fish to move between Hattah Lakes and the River Murray Provide spawning and recruitment habitat for small-bodied native fish and nursery habitat for large-bodied natives (such as golden perch)

¹The Hattah Lakes pumps station may also be operated at any time of year to meet maintenance requirements.

²Includes the following lakes: Bulla, Hattah, Little Hattah, Lockie, Yelwell and Yerang.

Engagement

Table 2 shows the partners and stakeholder organisations who have assisted the Mallee CMA prepare the Hattah Lakes 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 the Mallee Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Hattah Lakes seasonal watering proposal

Partner and stakeholder engagement
Individual landholders Individual small business owners 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 Goulburn-Murray Water Mildura Birdlife Club Sunraysia Bushwalkers Latje Latje Traditional Owners Munutunga Traditional Owners Tati Tati Traditional Owners Wadi Wadi Traditional Owners

Partner and stakeholder engagement

Individual landholders
Individual small business owners
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
Goulburn-Murray Water
Mildura Birdlife Club
Sunraysia Bushwalkers
Latje Latje Traditional Owners
Munutunga Traditional Owners
Tati Tati Traditional Owners
Wadi Wadi Traditional Owners