Lagarosiphon major

Lagarosiphon, Oxygen weed

Family: Hydrocharitaceae

Origin: South Africa

Lagarosiphon growing underwater and close up of stem.
Aquatic weed forming dense mats on stream and pond floors. Can block waterways and increase flooding likelihoods.
Photo credit: Rohan Wells, NIWA

Regional Pest Management Plan (RPMP) status

  • Aotea — Exclusion
  • National Pest Plant Accord Species
  • Whole region — Sustained control

View more about the RPMP statuses

General description

Bottom-rooted submerged perennial aquatic herb. Stems are < 2 m long and branching. Leaves are < 16 x 2 mm, curved downwards and arranged spirally around stem. Flowers are minute and pink.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell lagarosiphon. As lagarosiphon is a National Pest Plant Accord species, these restrictions apply within the Auckland region and across the whole of New Zealand.
  • You must not plant lagarosiphon within the Auckland region.
  • You must destroy any lagarosiphon on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

If you see lagarosiphon anywhere on Aotea/Great Barrier Island group, please report it to Auckland Council at


Static to moderately fast-flowing freshwater bodies < 6.5 m deep.


Vegetative spread from stem fragments, dispersed by water movement. Human-mediated dispersal through contamination of boats, fishing gear and machinery and deliberate plantings.

Impact on environment

Forms dense stands, displacing native aquatic herb species, altering habitat availability for fish and invertebrates, and affecting dissolved oxygen levels. Can impede recreational water access to water bodies.


Site Management

Very difficult to control once established. Consider an aquatic pest plant control operator. Contact Auckland Council for control options. Spraying aquatic weeds result in plants rotting in the water. This decreases dissolved oxygen in the water and in large amounts can kill aquatic life. Consider pulling out and only spraying regrowth in spring.

Recommended approaches

Do not attempt to undertake control of this species on Aotea / Great Barrier Island group. Please report to Auckland Council if seen on Aotea / Great Barrier Island group.

Physical control

Method: Pull out.

Plant parts requiring disposal: All parts.

Disposal options: Remove to greenwaste or landfill if practical.


Biocontrol is currently not available for this species.

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