‘Just keep multiplying’: Masterplan to determine fate of invasive lilies

There’s no long-term solution to a Cairns waterway choked by an invasive waterlily species despite a $35,000 council spend and renewed calls from one resident to completely eradicate the plant.

There’s no long term solution to a Cairns waterway choked by an invasive waterlily species despite renewed calls from a frustrated resident for council to completely eradicate the plant from Centenary Lakes.

In mid-2021 Cairns Regional Council spent an estimated $35,000 to secure the services of a specialist aqua harvesting team at the Greenslopes St nature area.

This followed a previous council statement saying there was “no intention to remove the lilies”.

Lilies growing at Centenary Lakes on Greenslopes St. Picture Nuno Avendano

But not all the plants were removed and six months later the surface of the water was again completely covered by the plant, according to resident Trevor Johnston.

Mr Johnston claims a silt build up on the bottom of the lake is producing methane gas and ruining what he says ought to be a “pristine” area.

“It stinks, the methane. It must be coming out of the silt in the lake,” he said.

“They have not maintained it, they are not native and they don’t die off they just keep multiplying.

Local resident Trevor Johnston has long advocated for the removal of the waterlilies. Picture: Brendan Radke

“It’s just not the way it’s supposed to be, it’s meant to be pristine clean water, those lilies should not be there at all.”

Late last year council director lifestyle and community Destry Puia agreed the build-up of silt since the lake was established in 1975 was a factor in the growth of the lotus species.

“(Silt build-up) has allowed the non-invasive and cultural significant lotus to flourish, although its spread has been inhibited recently by the invasive weed frogbit, which is now also prevalent in the lake,” she said.

A review of the Cairns Botanic Gardens masterplan is currently underway. Picture Nuno Avendano

“Council is spraying the frogbit, which will also kill the grass, but this could allow the lotus to continue spreading.”

A plan to manage the long-term maintenance and control of lotus in the lakes will be outlined in the Botanic Gardens Master Plan.

“Until the recommendations of the master plan are considered by council, which is likely to be early 2023, there are no plans to contract the surface-based aquatic weed harvester,” Ms Puia said.

In 2021 Cairns Regional Council hired contractors to remove an invasive species of waterlily that had completely covered the surface at Centenary Lakes. Brendan Radke

“Manual removal of lotus stems and pads will continue as part of routine maintenance.”

However Mr Johnston believes the current state of the lake is a missed opportunity to create a beautiful space and provide a healthy ecosystem for birdlife.

“They know the silt is there, they know the silt is a metre deep and they will give all kinds of excuses as to why they won’t do anything about it,” he said.

“It was a dead waste, an absolute waste.”

The review of the masterplan will determine which elements of the strategy should be retained, changed or removed. A public survey inviting feedback on the Cairns Botanic Gardens, Centenary Lakes and Tanks Master Plan closed on March 14.

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Originally published as ‘Just keep multiplying’: Masterplan to determine fate of invasive lilies