A Brazilian weed-eating weevil is being introduced to Forest Lake in a long-term attempt to remove the entrenched salvinia weed, which has choked the lake and poisoned hundreds of kilograms of fish.
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“It is natural pest which can chomp its way through and kill the actual plant itself so it sinks to the bottom of the lake,” local councillor Charles Strunk said.
“Both the plant itself and the weevil came in from Brazil. Both the plant itself and the weevil were introduced by us, human beings. So we were not thinking too clearly.”
Salvinia is classified as one of Australia’s worst choking weeds.
Forest Lake, built by Lendlease in the 1980s and 1990s, has 22,000 residents, many of them lured by the prospect of canoeing and paddling on the master-planned community's 20-hectare lake.
Lendlease finished its contract in 2000 and the lake is now managed by Brisbane City Council.
Early in November, the weed in Forest Lake was so thick it looked like lawn.
In August, about 700 kilograms of dead fish was pulled out after cold water in Forest Lake killed the tilapia fish.
Tilapia is an introduced fish from the Nile Valley and not used to cold weather.
Later Cr Strunk saw 35 dead fish floating on the lake.
“They [the council] did a number of tests on water quality with regard to the algae, the oxygen levels and a few other tests to make sure the environment wasn't killing the fish, such as poison,” he said.
“They have decided that what has happened is that the temperature of the lake got low enough the tilapia couldn’t survive.”
Cr Strunk said he wrote to lord mayor Graham Quirk and the former council opposition leader, federal Oxley MP Milton Dick, to take action.
“Within a few days, things started to happen,” Cr Strunk said.
“It is an ongoing issue to clean the lake because it is a still body of water that needs and requires outflow and we need rain.
“So, consequently, it’s a huge challenge to keep on top of that with the blue green algae, the salvinia - the weed growing up from the bottom – and it’s just a big challenge.”
Contractors were now in their second week of removing salvinia weed from the lake, Cr Strunk said.
“Hopefully all of the salvinia will have been cleared from the lake at the end of this week,” he said.
Cr Strunk said it cost the council $50,000 a year to maintain Forest Lake.
Cr Strunk said salvinia weed was also a problem in a lagoon in Deagon.
“Anywhere there is a still body of water, it is a problem. It can double in size within two to three days if the nutrients and weather conditions are right,” he said.
More than 2200 Forest Lake residents signed a petition in July asking for action to remove the choking weed.
