Lake Mulwala will be lowered by about 3.5 metres this winter to facilitate works around the lake foreshore and to control weed.
After much speculation in recent months Murray–Darling Basin Authority (MDBA) and Goulburn-Murray Water (GMW) confirmed last Friday the lake would start to be emptied at the end of April and be full again by early August.
Authorities have committed to lowering the lake every few years to mainly control the invasive aquatic weed, Egeria densa.
In the last 10 years Lake Mulwala has been lowered four times in 2008, 2009, 2011 and again in 2015.
Victorian Department of Primary Industries expert Dr Tony Dugdale told the Chronicle in 2011 it was “unlikely Lake Mulwala will ever be rid of Egeria densa”.
“Not unless something completely out of the ordinary or unexpected happened. Drawing down the water in the lake to expose the Egeria to air is the most effective and readily available method of control,” Dr Dugdaale said.
In an economic boon for Yarrawonga Mulwala the advanced notice of the drawdown in 2015 allowed time to plan more than an estimated $1 million in public and private works in and around the lake.
Works included the construction and repair of major retaining walls, building of around 30 jetties, erosion control works and the maintenance of boat ramps.
GMW General Manager Customer Operations, Scott Barber, said that winter draw-down was important because it enables structural works to be undertaken around the lake.
“We’ll use this opportunity to upgrade the retaining wall along the Yarrawonga foreshore and look to assess and improve boat ramps if needed,” Mr Barber said.
“The main reason for the winter draw-down is to control the extensive build-up of the highly invasive aquatic weed Egeria densa which can displace native submersed vegetation and impacts on the lake’s usage, making it harder to swim, fish, launch boats and water ski.
“We have listened and taken on-board community feedback about the build-up of the aquatic weed in the lake and suggestions of a drawdown this year to reduce the weeds impact on recreational activities.
“Previous winter draw-downs have proved effective in controlling the waterweed which dies off as it dries out and when exposed to frost.”
MDBA’s head of River Management, Andrew Reynolds said the lake will be back to its usual level in early August.
“Lake levels will start to fall slowly from 30 April by about 70cm until mid-May when the irrigation season ends,” Mr Reynolds said
“Once we are sure that irrigation water delivery to customers is finished for the year, we’ll accelerate the drawdown until Lake Mulwala is 3.5 metres lower than normal—a level we expect to hold until mid-July when refilling will start.
“The drawdown will be managed in a way that poses minimal risk of impacting on available water resources in the coming season.
“I recognise that Lake Mulwala is important to the local community and that any significant change in the lake level may have social and economic effects,” Mr Reynolds said.
“The lowering will expose the lake flats, which will be muddy, reducing amenity, access and the ability to launch boats from the boat ramps. People will still be able to boat and fish in the main river channel that runs through the lake but will need to launch their boats upstream.
“Along with GMW we have been talking with community members, council and tourism operators to try to minimise and limit disruptions.”
Last year GMW and the MDBA released the Waterweed Wipeout app. The tool is designed to help the community better understand the management techniques used to control the invasive weed. Waterweed Wipeout is free and available from the App Store and Google Play for Apple and Android phones and tablet devices.
In accordance with the longstanding Murray–Darling Basin Agreement, River Murray operations assets are owned by a ‘Joint Venture’ comprising of basin state and federal governments. The MDBA is tasked to operate the River Murray system on behalf of the Joint Venture. GMW is the state constructing authority responsible for managing and maintaining Lake Mulwala under the direction of the MDBA.