Egeria densa (syn. Anacharis densa; Elodea densa)

Also known as: Oxygen weed, Brazilian waterweed
Pest group: Freshwater | Plants
Pest type: Waterway plants

Egeria is a bottom-rooted, submerged, perennial aquatic herb with green leaves and white flowers. It alters the habitat structure of macroinvertebrates and fish and displaces native plants.


  • Stems are long and leaves are about 30x5mm, in whorls of four to five.
  • Flowers are white and borne at the water’s surface between November and January.
  • Vegetative spread from stem fragments, dispersed by water.
  • Human-mediated dispersal through contamination of machinery and equipment and deliberate plantings.
  • Habitat is static to moderately flowing water bodies less than 8m deep.

What you need to know

Forms dense stands, displacing native aquatic plants and altering the habitat structure of macroinvertebrates and fish. Can lower dissolved oxygen levels, increase sedimentation, and alter the primary production and nutrient cycling capacity of water bodies.

Management approach

This is a declared pest managed under the Canterbury Regional Management Plan 2018 – 2038 (PDF file, 10.6MB) within the eradication programme.


Pests in the eradication programme are present in low numbers or have limited distribution within Waitaha/Canterbury and eradication is feasible.

The community should make us aware of any egeria plants in Waitaha/Canterbury. We will work with affected landowners to undertake control of egeria.

Egeria is also an unwanted organism regulated under the National Plant Pest Accord.


Any species declared a pest cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread.


Do not attempt to undertake control of egeria yourself. Report any sightings to us.