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Forest Lake, built by Lendlease in the 1980s and 1990s, now has 22,000 residents, many of them lured by the thoughts of canoeing and paddling through the 20-hectare lake.
Lendlease finished its contract in 2000 and the lake is now managed by Brisbane City Council.
A fortnight ago, the weed in Forest Lake was so thick it looked like lawn. In late July, weed growth and cold water temperatures resulted in 800 kilograms of dead fish being removed by excavators from Forest Lake.
Tilapia are an introduced fish from the Nile Valley and not used to cold weather.
Cr Strunk said he had to write to lord mayor Graham Quirk and the former council opposition leader, federal Oxley MP Milton Dick, for action to take place.
“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 over-grown salvinia weed from Forest Lake, Cr Strunk said.
Salvinia weed begins to reduce at Forest Lake as contractors begin to remove the choking weed.
“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.
Forest Lake on November 20, 2018 after contractors have almost removed the salvinia weed from the 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.
In August, about 700 kilograms of dead fish was pulled out after cold water in Forest Lake killed the tilapia fish.
Later Cr Strunk saw a further 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.”
A majority of the dead fish were the pest fish tilapia.Credit:Pest Fishing Adventures
More than 2200 Forest Lake residents signed a petition in July asking for action to remove the choking weed.
Tony Moore is a senior reporter at the Brisbane Times