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Published: 16 March 2009   •   Media release

The Murray–Darling Basin Authority, in conjunction with Goulburn–Murray Water, is planning a drawdown of Lake Mulwala in late autumn and winter to control the spread of an invasive aquatic weed.

Egeria densa, commonly known as dense waterweed, is a non-native weed introduced from South America that has formed dense clumps throughout Lake Mulwala. It is affecting recreational and tourism activities, interrupting normal operation of the power station and fishway at Yarrawonga Weir and causing problems for town water supplies.

There are a number of control methods available; however, a lowering of the water level is the only method that provides viable weed control over the whole of the Lake.

The lake has been subject to winter drawdowns at irregular intervals, ever since it was constructed. The most recent were; 1984, 1989, 1993, 2002 and a partial drawdown in 2008.

It is understood that the local community is generally supportive and recognises that an ‘off season’ lowering will provide recreational and tourism benefits for a number of years.

The first phase of the lowering is planned to commence in late April. Irrigation diversions will not be affected. The water level will be gradually lowered, up to 10 cm each day, until the lake level is about 123.5 m AHD (or 1.4 m below Full Supply Level) by the end of the irrigation season in mid-May.

After the end of the irrigation season, the rate of drawdown would be accelerated by increasing the release from Yarrawonga Weir. The rate of drawdown would up to about 30 cm/day. The lake level would be lowered to about 119.5 m AHD (or 5.4 m below FSL) by early June and held constant until about mid July.

Refilling is expected to begin in mid-July, and the water level would be raised to a level which allows irrigation diversions at the start of the irrigation season in early to mid-August.

This current plan may be altered in response to weather and river conditions over the coming months. Further updates will be provided in media releases and in the MDBA’s weekly report prior to, and during, the drawdown.

 

Media contact: MDBA, Sam Leone, phone (02) 6279 0141

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