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Wednesday, April 21, 2021

Floating wetlands make a splash in Lake Tuggeranong

Floating wetlands have been launched (literally) in Lake Tuggeranong in a two-year trial to clean up blue-green algae. The lake was closed earlier this month after an extreme alert was issued for the algae, which can cause diarrhœa in humans and kill animals.

The three floating wetlands are in the Village Creek embayment, Kambah, identified as “the number one hotspot”, Shane Rattenbury, Minister for Water, said. The channel is a key source of nutrients that feed algal blooms, but the wetlands will act as a barrier. Native plants on them will “soak up” (capture) the nutrients, and stop them from flowing into the lake.

“These floating wetlands will compete for both nutrients and light with the algae, and hopefully suppress the algae,” ACT Healthy Waterways program manager Dr Ralph Ogden said.

Floating wetlands. Picture: Nick Fuller

Nearby, a gross pollutant trap causes some of the algae trouble. Although it traps leaves, grass and other organic matter – as it is meant to do – the detritus is stewing in the summer, and releasing the nutrients into the lake when flows are low and the temperature hot, Dr Ogden said.

“That’s a perfect environment for algae to begin to bloom, and then they can get washed into the lake,” he said.

In fact, more nutrient pollution is coming out of the trap than coming in.

The wetlands are made from recycled plastic with a mat of coir (coconut fibre), native plants considered suitable for Canberra extremes on top, their roots growing through the material into the water. A UV coating preserves the plastic from degradation.

“They’re rated at 50 years; they’ll be here for a while,” Dr Ogden said.

The wetlands cover half a square kilometre. Cables secure them to the shore far enough away to deter “adventurous young types”, Mr Rattenbury said.

Young plants on the floating wetlands; they will grow rapidly within the year, soaking up nutrients. Picture: Nick Fuller

This is the first large-scale deployment of floating wetlands in the ACT, but similar wetlands have been used worldwide. If successful, the wetlands will become a permanent fixture in Lake Tuggeranong. Plants will bloom within a year.

However, Dr Ogden said this would be part of many mechanisms to lower nutrient loads. “There’s not going to be a single solution.”

Glenys Patulny, chair of the Southern ACT Catchment Group and convenor of the Tuggeranong Lake and Catchment Carers, was pleased to see the wetlands; even if they had only a minor effect, they would contribute to cleaning up the lake. “Hopefully in the long run, we’ll be able to use the Lake the way it was meant to be used.”

Mr Rattenbury said he wanted to see Canberrans kayaking, windsurfing and swimming in the lake once more. He assured the Tuggeranong community the ACT Government was committed to improving water quality.

“We think the measures that have been put in place now will begin to turn this problem around. I don’t think we will see an instant fix, but we will see a steady improvement in the water quality in Lake Tuggeranong.”

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