Bay of Plenty Regional Council is urging people not to grow or share aquatic pest plants because of the risk posed to waterways.
The council says it's particularly concerned about salvinia, also known as kariba weed, and water hyacinth, which have been found in farm ponds and other waterways.
Both weeds are present in the region and are known for growing rapidly to form large dense floating mats, which can double in size within days.
They pose flooding risks and the risk of drowning to humans and livestock caught in them.
The council is concerned the weeds are being propagated and distributed among pond growers.
It says the plants have been declared unwanted and are notifiable organisms under the Biosecurity Act.