The reappearance of the noxious seaweed caulerpa taxifolia in Lake Macquarie has alarmed nature lovers, however, authorities are reluctant to act.
Caulerpa is a native to tropical waters off the Queensland coast, but is considered a noxious species in NSW.
Its feather-like fronds grow rapidly, smothering local species of seagrass in the process.
The so-called "killer weed" made international headlines in 2001 when it was found to have choked thousands of hectares of Mediterranean seabed.
Sea turtle enthusiast Alison Dunn spotted the noxious species growing in shallow water at Wombal Reserve Coal Point this week.
"I was out on the jetty and it was sort of glowing. I thought that's not paddle weed, which is what the turtles like to eat," she said.
"As I went out I saw more clumps of it."
Large quantities of salt were used to kill-off the weed when it was first identified in Lake Macquarie in 2001.
It reappeared at Green Point 2016, however, authorities were not as alarmed as they previously were.
A Lake Macquarie Council spokesman said photos taken by Ms Dunn this week appeared to show Caulerpa taxifolia. The council referred the matter to the Department of Primary Industries.
A department spokeswoman said outbreaks of Caulerpa were almost impossible to eradicate.
"They require extensive resources and it cannot be guaranteed that Caulerpa will not reoccur," she said.
She said the department focused its control efforts on preventing the spread of the weed to unaffected estuaries, rather than on activities that have minimal impact on established populations.
"We encourage people in the Lake Macquarie region to 'Make clean part of your routine' by checking for Caulerpa when fishing and boating and safely disposing of it, by placing in a plastic bag and disposing of it in general waste," the spokeswoman said.
Fishers and boaters are urged to clean their gear and equipment before leaving affected estuaries to minimise the risk of further spread.
Ms Dunn said a greater effort should be put into educating the public about the weed's damaging impacts.
"When there are big boating events on or there are jet skis getting around, cutting up threatened and endangered seagrass is a serious matter," she said.
"Is a noxious weed that needs to be taken seriously."
