Isaac Regional Council grappling with salvinia weed at Clermont

Salvinia molesta, a free-floating aquatic fern, has engulfed Clermont's star tourist attraction, Hood's Lagoon in recent months, much to the dismay of locals and visitors alike.

The plant is a Weed of National Significance thanks to the way it reduces oxygen levels in the water, affecting water quality, wreaking havoc on irrigation systems, creating an ideal breading grounds for mosquitoes and non-native fish, and being a drowning threat to animals and wildlife.

The council has been aware of the problem since at least March, and immediately engaged Biosecurity Queensland and other local governments to understand best practices, beginning strategic spraying in May along with mechanical removal of large dense shallow mats.

At the end of November, the council secured the services of an aquatic harvester to undertake the large-scale mechanical removal of the floating mass.

According to a council media release, sourcing the machine had been a challenge, due to the numerous other local governments and state government agencies also battling with salvinia weed infestations.

It says the contractor will be at work for 10 days on the job.

"Following removal from the lagoon, the salvinia will be transported to a disposal area adjacent to Charles Street where it will remain until it breaks down and is no longer a biosecurity risk," the release states.

"Other areas of Hoods Lagoon will remain open during this process, however the public is asked to follow signage and not enter the cordoned off disposal area where the weed will be stockpiled.

"Salvinia is a restricted plant under the Biosecurity Act 2014 and removal of the plant is an offence."

Questions have been asked about the disposal site and whether it's out of flood areas, to which council has responded that officers were monitoring the 28 day weather forecast.

"We will be accelerating the decomposition of the weed to ensure it is destroyed appropriately," a spokesperson said.

People have also been assured that weed that escaped downstream had been sprayed and was being monitored, along with mesh fences being installed to prevent further escapes.

"All current inspections have shown the escape weed has died," the spokesperson said.

Once the majority of the weed has been sucked out of the lagoon, the Isaac council will use two skimmers to remove smaller remaining sections of weed.

It's one of a number of ways of attacking the problem going forward, which includes the application of registered herbicides, and the introduction of locally bred weevils.

The latter are not expected to produce instant results, taking up to two years to reduce an infestation.

PVC pipes are housing the weevils and residents have been asked not to retrieve them if they notice them.

According to a public update, spraying of salvinia in the gully downstream from the lagoon has been effective, but monitoring continues.

While not pinpointing a source that started the growth, Isaac Regional Council communications have been encouraging residents to not dispose home aquarium and pond plants into the waterways.

A spokesperson said it was council's understanding, including officers that have been in the town for more than a decade, that it's the first time the weed has invaded Hoods Lagoon.

Environmental consultant Ian Read, based at Bundaberg, said floods often washed the weed from one waterway to another.

"It's not sold in the aquarium trade these days," he said. "It can be spread by vehicles, or most commonly by water, such as water trucks."

He said the secret to containing salvinia was getting onto it early.

"It has a severe effect on the environment, and a treatment such as spraying is a balance between the damage that's being done and pesticides that aren't environmentally friendly.

"Control can cost millions of dollars - community education programs can be very beneficial in these circumstances."

Isaac's community updates acknowledge that ongoing monitoring and follow-up treatments will be required over multiple years to remove the invasive species from Hoods Lagoon.

"Council shares the same community frustration," it says.

"Control programs on large infestations are very intensive and require a multi-year commitment.

"Residents might not see a council officer at the sites however we are working hard to limit the impacts of salvinia weed."

Council says the projected cost of the weed management program is under $50,000, which includes the cost of spraying, manual removal and the localised weevil breeding program.

Property owners are reminded to be vigilant and if they suspect salvinia on their property, are asked to contact the council's customer service centre on 1300 ISAACS (1300 47 22 27) for identification and information.

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