Muddy Lake Ecosystem

Dora Creek's Muddy Lake is a small body of water that has had a big problem with a tiny solution. Muddy Lake used to benefit from the salt water that entered through a small inlet off Lake Eraring. Over a relatively short time, mangroves came to effectively block off that flow. They have greatly reduced the movement of salt water into this protected waterway. As a relatively protected area of water, Muddy Lake is a particularly high-value conservation area. Its wetlands provide a home for many water birds and amphibians, including green and gold bell frogs. With the change in the flow of saline water into the bay, conditions became perfect for the invasive water weed Salvinia molesta to take hold and choke off much of the waterway.

Salvinia has been identified as a Weed of National Significance. It is regarded as one of the very worst weeds due to its invasiveness, potential to spread and severe environmental impacts. The weed grows rapidly to form a dense mat of vegetation that blocks sunlight and oxygen, chokes waterways and negatively impacts aquatic life. In ideal conditions, it can double in size every three days. Salvinia has been growing on Muddy Lake since 2020. It quickly took over approximately 20 hectares and made Muddy Lake look like a vast green field rather than a waterway. Locals take the view that you can go and rip it out. Indeed, I often hear that refrain. If only it were so easy.

A host of native flora and fauna are now thriving in the new conditions, including the endangered green and golden bell frog. Crown Lands and council officers agree that restoration of the saltwater influence would kill the weed, but at those levels it would also kill the frogs. Both species need more fresh water than salt water to flourish. Protecting the ecosystem of the lake is therefore a biological balancing act. In 2020, biosecurity staff at Lake Macquarie City Council and the NSW Department of Primary Industries and Regional Development collaborated to tackle the issue. They have employed the services of a tiny warrior which was provided by the Grafton biocontrol centre. I introduce cyrtobagous salviniae. These tiny weevils are bio-assassins. Their numbers grow when their favourite food, salvinia, is in abundance. They decimate new growth.

Locals have witnessed the weevils' handiwork over the past couple of years as the surface of the water has begun to see sunlight. The weevil has kept the weed infestation at relatively low levels in the open water. However, salvinia still persists in the shallow backwater areas of the wetland system. Warm weather and fresh rainfall created perfect conditions during the growth season and gave the weed an opportunity to gain some ground on the battlefield. But as the weed grows, so too does the weevil population. The weevils will now be redeployed to take up the good fight again. I thank our local council and the State Government for the innovative work to protect Lake Macquarie's valuable mangrove habitat and unique biodiversity.

I also acknowledge the work of Lake Macquarie City Council in supporting local landowners to tackle salvinia infestations in water bodies on private lands. It is no secret that we are seeing more development in Lake Macquarie. In the face of more residential, industrial and commercial growth, it must be remembered that one of our main drawcards is our natural environment. It is a key reason why we love living locally. It is part of the identity of the lake residents. We must ensure that growth of our built environment is sustainable and that environmental wellbeing is not forgotten or neglected. To do so would be to undermine the very reason so many of us choose to live in this great location. I once again thank Lake Macquarie City Council, the Department of Primary Industries and Regional Development and local residents for their efforts to address the scourge of salvinia.