10-07-2025
Invasive Amazon frogbit weed found for first time in the Northern Territory
One of the "world's worst weeds" that can threaten drinking water supplies and clog irrigation channels has been discovered in Darwin.
Amazon frogbit is a fast-growing, floating aquatic plant that can grow half a metre deep in rivers.
This is the first discovery of the plant in the Northern Territory, where it is a declared a weed that should not be introduced.
The frogbit was spotted in a social media post from someone living in Darwin's northern suburbs, NT weeds officer Peter Ross said.
"He wasn't sure what type of plant it was and whether anyone knew what it was," Mr Ross said.
Frogbit was brought into Australia decades ago as an ornamental plant for fishponds, tanks and aquariums.
The plant has smooth, round leaves about the size of a 10-cent coin, and occasional small white flowers.
Reece Pianta from the Invasive Species Council said a lot of people thought it looked quite nice.
"The problem is if it gets out into nature — into a creek or a dam — it will take over that water body, and it will form a thick layer of frogbit on the top," he said.
Dense frogbit infestations will rot in the water, which weed specialists say poses a risk to drinking water supplies.
There are so far no reports that the weed has spread beyond the suburban fishpond in Darwin.
But the Northern Territory's land and environment department has described it as "one of the world's worst weeds".
"I would back that assessment," Mr Pianta said.
"It becomes a problem for irrigation equipment, we've even had an example where it's impacted a hydro-electric project in Far North Queensland.
"It costs hundreds of thousands of dollars for councils, and Indigenous ranger groups, and Landcare organisations to manage this problem."
Despite being highly invasive and regulated in several states and territories, Amazon frogbit is available in Australia through online stores and marketplaces.
Plants are for sale for between $6 and $9.
Just one online aquatic plant store visited by the ABC carried a warning that frogbit could not be sold in New South Wales because it was a declared noxious weed.
Mr Pianta said stronger regulation was needed to stop frogbit from being sold or traded.
"It isn't restricted in Queensland, where it was first discovered."
He said better consumer education was needed to help prevent the spread of invasive weeds.
"One of the main things that we need people to do is switch on to what they're buying," Mr Pianta said.
"But we also need stronger regulation on the sectors that are selling and trading these products."
The NT Department of Lands, Planning and Environment is urging anyone who suspects they have seen Amazon frogbit anywhere in the territory to contact its weed management branch.
