Botanic Garden lagoon choked by weeds
Birdlife Mackay president says bird, fish numbers have declined but Council says they are ‘healthy’
Mackay
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THE lagoon viewed from the Mackay Botanic Garden's observation deck is largely weed-free but either side remains choked by the invasive weeds.
It is an ongoing issue for the Mackay Regional Council which began fortnightly spraying herbicides and using a long-arm excavator to mechanically remove the weeds.
MRC development services director Aletta Nugent said council was also piloting a desilting project and was waiting on a weevil order.
"At this stage, we are hoping to have weevils delivered in September when the weather warms up," she said.
"We currently don't have the resources available to construct or manage the growing ponds that would be required to produce our own".
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Birdlife Mackay president Daryl Barnes said spraying the weeds could be having a flow-on effect on the food chain by sinking to the bottom and then using up the oxygen in the water as they decomposed.
He said the group's monthly survey showed bird numbers had declined since the weeds took over but they had seen two platypus return since the council cleared the section below he cafe.
A physical bunting barrier has been installed around the area to prevent weeds from re-entering.
But Mr Barnes said they were yet to see the higher trophic bird species like the cormorants or pelicans return to the lagoons.
"If there was a healthy population of fish, you'd have birds here feeding on them and that's not happening yet," Mr Barnes said.
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Ms Nugent said fish and bird numbers remained at a "healthy" level.
"And there is always more than one single factor to consider when attributing cause and effect," Ms Nugent said.
She said the three main problematic weeds the Council faced at the lagoons were the Water Hyacinth, Salvinia and Water Lettuce.
All three are 'restricted invasive plants' under Queensland's Biosecurity Act 2014; the first two provide breeding grounds for mosquitoes but all contribute to water loss, destroying native habitats and depleting oxygen in the water - which is detrimental to aquatic ecosystems.
Mackay resident Graeme Ransley said he was concerned birds had spread the pest weeds elsewhere.
"I've noticed the small lagoons near the (South Sea) Islander Hut that were free of weeds before, are now totally covered in weeds," Mr Ransley said.
"It's spreading all over as far as Kinchant Dam and numerous waterways."
Ms Nugent said desilting of the lagoon will increase the water depth and help to reduce further weed incursion.
"The weeds in the Botanic Gardens lagoons have reduced their spread substantially over the last month due to a cool change in the weather ..... the desilting pilot trials will be continuing in 2020 and it could take up to a year to see results."
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