The Ministry for Primary Industries (MPI) and Auckland Council want the public's help to contain two of the "world's worst weeds".
Water hyacinth and salvinia are both present in Auckland and are known for growing rapidly to form large dense floating mats on ponds, drains, lakes and swamps that can clog waterways and lead to drowning.
MPI response manager Emmanuel Yamoah said the two weeds were among the world's worst and grew rapidly, able to double their population size in less than two weeks.
The weeds had the potential to damage waterways, native aquatic plants and fish, Yamoah said.
"They can clog waterways, making almost all water activities impossible and increasing the danger of drowning to humans and livestock," he said.
The weeds also had adverse impacts on hydro-electricity generation and irrigation.
MPI and Auckland Council had an eradication programme in place for the weeds but wanted residents to report any fresh sightings.
Yamoah said home and farm ponds around Auckland had been cleared of the noxious weeds, thanks to reports form the public.
Salvinia is a small, free-floating aquatic fern with branched, horizontal stems that lie just below the surface.
The upper surface of the leaf is covered with white hairs and it has a root-like structure underneath each leaf pair. As the plant matures, these roots resemble wet hair.
Water hyacinth is a floating aquatic perennial, with bladder-like swollen leaf stems giving it buoyancy.
It has shiny rounded leaves with thick masses of feathery dark roots that can reach 2.5 metres in length and produces mauve-blue flowers with a yellow spot.
It is illegal to share, grow or sell unwanted and notifiable organisms, such as these weeds, under the Biosecurity Act.
Anyone who sees these weeds, or suspects they may be present, should report it to MPI on 0800 80 99 66.
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