Full lake for win­ter

Yarrawonga Chronicle - - Front Page - BY RACHEAL WILLETT.

The Mur­ray Dar­ling Basin Author­ity has con­firmed Lake Mul­wala will not be drawn down this win­ter with the lat­est weed sur­vey re­port show­ing there is no need to do so.

Lake Mul­wala is some­times drawn down dur­ing the win­ter when reg­u­lar sur­veys of the aquatic weed Ege­ria densa point to a need to ex­pose the lake bed to air and frost to con­trol the weed growth.

In early April, MDBA Gen­eral Man­ager An­drew Reynolds told the Yar­ra­wonga Chronicle, “when last sur­veyed in 2016 we did not ex­pect to need to lower the wa­ter level this year, but weed growth ap­pears to have been greater in the past year than we have seen pre­vi­ously”.

Mr Reynolds said com­mu­nity ad­vice cor­rob­o­rated the sug­ges­tion of in­creased weed growth so a fi­nal de­ci­sion on whether the lake would need to be low­ered this year would hinge on a weed sur­vey to be un­der­taken later in April.

Late last week an MDBA spokesper­son pro­vided de­tail to the Yar­ra­wonga Chronicle of the most re­cent weed sur­vey.

“This year’s sur­vey of Lake Mul­wala again sam­pled 165 sites dis­trib­uted across the lake. An un­der­wa­ter video cam­era was used to de­tect Ege­ria as well as na­tive aquatic veg­e­ta­tion in the lake,” the spokesper­son said.

“The sur­vey has shown that while Ege­ria has in­creased over the last year, there is no need to lower Lake Mul­wala at this time.

“The re­sults are con­sis­tent with our aim of keep­ing the lower basin around Mul­wala and Yar­ra­wonga rel­a­tively weed free for re­cre­ation. “

The spokesper­son pointed out that aquatic veg­e­ta­tion was im­por­tant to the lake’s

ecosys­tem, in­clud­ing to pro­vide habi­tat for fish, so al­low­ing some re­growth was ben­e­fi­cial.

“While the sur­vey showed an in­crease in Ege­ria in the mid and up­per reaches of the Lake, it also re­vealed an in­crease in na­tive species.

“With the over­all abun­dance at low to medium lev­els, a low­er­ing of the lake again is not yet war­ranted.

“Given the in­crease in Ege­ria, a low­er­ing of Lake Mul­wala in 2018 may be ben­e­fi­cial. MDBA will con­sider the Ege­ria sit­u­a­tion along with other lo­cal and sys­tem-wide fac­tors be­fore ad­vis­ing of a fi­nal de­ci­sion in the lead up to win­ter 2018.”

Lake Mul­wala was last low­ered dur­ing the win­ter of 2015. That year the de­ci­sion was made early in Fe­bru­ary be­cause the draw- down was re­quired to fa­cil­i­tate work on the Yar­ra­wonga Weir wall as well as as­sist with weed con­trol.

In an eco­nomic boon for Yar­ra­wonga Mul­wala the ad­vanced no­tice of the draw­down 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.

The works were co-or­di­nated in part­ner­ship with the MDBA by Goul­burn Mur­ray Wa­ter and many res­i­dents took the op­por­tu­nity to ob­tain per­mits for jet­ties while a mora­to­rium was tem­po­rar­ily lifted.

Or­di­nar­ily a de­ci­sion on whether or not to lower Lake Mul­wala isn’t made un­til April, once the MDBA has the lat­est weed sur­vey re­sults.

Lake Mul­wala was low­ered in 2008, 2009, 2011 and in 2015.

Ege­ria densa, com­monly known as dense wa­ter­weed, is a non-na­tive plant that forms dense clumps in Lake Mul­wala.

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.

Once an area of Ege­ria is ex­posed to air and frost, it then takes an un­de­fined pe­riod of time for the weed to re­cover which in turn dic­tates when the next draw­down is needed.

This win­ter Lake Mul­wala will re­main full af­ter the MDBA de­ter­mined there was no need to lower the wa­ter as a weed con­trol mea­sure.

Th­ese are im­ma­ture strands of Ege­ria densa, a wa­ter weed na­tive to South Amer­ica but now at home in Lake Mul­wala. The strands would be dou­ble this size by ma­tu­rity.

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