Najas guadalupensis

Southern naiad

Also known as:

Southern water nymph

Family: Hydrocharitaceae

Origin: North and South America

Southern naiad floating in the water.
A plant with slender stems and small elongated leaves with small flowers. Can form dense growths in waterways preventing recreational use.
Photo credit: Carl Pingry, Lady Bird Johnson Wildflower Center

Regional Pest Management Plan (RPMP) status

  • Unwanted organism

View more about the RPMP statuses

General description

Submerged aquatic. Stems slender, branching and < 90 cm long. Leaves are narrow, opposite or in whorls, toothed and tapered to a blunt or pointed tip. Flowers are small, inconspicuous and borne in leaf axils.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell southern naiad. As southern naiad is an Unwanted Organism, these restrictions apply within the Auckland region and across the whole of New Zealand.


Still or flowing freshwater bodies, lakes, stream, ponds, ditches.


Seeds dispersed by water. Vegetative spread from stem fragments. Human-mediated dispersal through movement of contaminated boats and equipment.

Impact on environment

Can form dense infestations, outcompeting native plants and clogging waterways.


Site Management

Consider engaging an aquatic pest plant control operator to control large infestations. Follow up treated areas each year.

Recommended approaches

Physical control

Method: Rake up and pull out between November and January.

Plant parts requiring disposal: All parts.

Disposal options: Leave onsite to rot down away from the water.


Biocontrol is currently not available for this species.

Community agrichemical control recommendations

Certified Handler/Experienced agrichemical user: Follow up in summer after pulling out plants with a foliar spray of 100 ml glyphosate green per 10 L of water.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Close up of southern naiad.
An aquatic weed that comes from America. It prefers to grow under the surface of water in ponds and lakes.
Photo credit: University of Florida, Center for Aquatic and Invasive Plants
A black and white drawing of southern naiad leaves.
Flowers do produce viable seed and this is moved about by water. If you break off a piece of stem this can float downstream and start growing.
Photo credit: University of Florida, Center for Aquatic and Invasive Plants