Lake Macquarie council uses weevils to battle Salvinia weed infestation at Muddy Lake

Crown Lands and Lake Macquarie council have banded together to try to control Salvinia weed, that has been growing on the 114 hectare Muddy Lake since late 2020.

Up to 25 hectares of the waterway has been infested with Salvinia, one of the country's worst for invasiveness, which can double in size every three days in ideal conditions.

Member for Lake Macquarie Greg Piper said Muddy Lake is home to wetlands, water birds and green and golden bell frogs and is an important ecosystem to keep healthy.

"This joint project will help us better understand the causes of the weed outbreak and hopefully lead to more ways to better manage it long-term," he said.

Muddy Lake is a high conservation area, and the issue with Salvinia is that it forms a dense mat on the water which blocks light and oxygen and threatens ecological health.

The council has released a tiny weevil, called Cyrtobagous salvinia, as a biological control agent which it argues has achieved strong results destroying the weed in the south-east of the lake.

Adult weevils feed on Salvinia while their larvae tunnel into the plant's stem, causing the weed to lose buoyancy and sink.

It's cleared large areas of the lake and a number of water birds have returned, and Lake Macquarie mayor Kay Fraser said it was great to see the partnership paying off.

"Muddy Lake looked more like a paddock than a waterway for a long time due to the Salvinia infestation, so it's very pleasing to see it returning to a much healthier state," she said.

"We'll continue looking at innovative ways to protect and preserve our environment."

While the weevils are doing their work, they aren't enough to eradicate the weed which could spread again as warm weather approaches ahead of summer.

Salvinia only survives when salinity levels are low, so natural saltwater flushing out of Muddy Lake could potentially help control the weed, however the lake faces salinity issues.

Muddy Lake is now largely disconnected from Lake Eraring and the broader estuary where high salinity levels naturally occur.

Mangroves and sediment act as a barrier but high tides and wet weather have reduced salinity levels, enabling the weed to grow.

Both Crown Lands and the council are working with the University of NSW's Water Research Laboratory to investigate options to reinstate tidal flows at Muddy Lake.

Other options to control the weed include manual removal which is expensive and ongoing, or the use of herbicide which could have negative impacts on the environment.

Minister for Lands and Property Steve Kamper said the lake is on a Crown waterway in Dora Creek.

"Crown Lands is a member of the Hunter Regional Weeds Committee with a duty to help control priority weeds, so it's great to see it working with Lake Macquarie City Council on ways to control the spread of Salvinia to protect this habitat," he said.

The weed has been growing on the lake since late 2020.

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