Najas marina


Family: Hydrocharitaceae

Origin: Cosmopolitan

Close up of sawtooth stems and submerged in waterway
Brittle slender stems with triangular prickly leaves. Tiny green flowers.

Regional Pest Management Plan (RPMP) status

  • Unwanted organism

View more about the RPMP statuses

General description

Submerged perennial aquatic. Stems are slender, brittle, branched and prickly. Leaves are triangularly toothed, prickly, < 45 mm long and opposite or in whorls of three. Flowers are tiny, green and borne in leaf axils. Achenes are plump and olive green/reddish.

What you need to know

To help protect our environment:

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


Saline and freshwater bodies, ponds, lakes, reservoirs, slow-moving streams


Seeds dispersed by waterfowl. Vegetative spread from fragments. Human-mediated dispersal through movement of contaminated ballast water.

Impact on environment

Forms dense mats, outcompeting and displacing other vegetation. Clogs and impedes access to waterways.


Site Management

Consider an aquatic pest plant control operator.

Recommended approaches

Physical control

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

Plant parts requiring disposal: All parts.

Disposal options: Leave on site 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.