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Water poppy (Hydrocleys nymphoides)

Water poppy is an introduced perennial aquatic weed that can form dense floating mats in waterways. These infestations can choke waterways, restrict water flow and access, and harm native aquatic plants and animals.

Key facts

Type: Weed, aquatic.

Native to: Central and South America.

Established in: QLD, NSW, VIC.

Identification

  • It is a perennial water plant with floating and emergent leaves, and stems that can grow several metres long.
  • Its dark green, shiny leaves are oval, round or heart-shaped, up to 13.5 cm long and 12 cm wide, and grow in rosettes that float or emerge up to 40 cm above the water.
  • Pale yellow, poppy-like flowers with a dark brownish-to-purple centre have three petals and are 5–8 cm wide.
  • Flowers grow above the water on stalks up to 30 cm long, while stems float below the surface and form tangled mats.
  • Roots can grow from stem nodes and into mud, usually around the shallower edges of waterways.

Where it grows

In Australia, water poppy is a weed in Queensland, New South Wales and Victoria, growing in still to slow-moving water such as waterways, lakes, swamps, shallow ponds, drainage channels and farm dams.

Why it matters

  • Dense infestations can block waterways and limit water flow, increasing flood risk.
  • They can reduce light and oxygen in the water and compete with native water plants.
  • They can reduce food and habitat for fish and other aquatic animals.
  • They can limit access to water for recreational use.

How it spreads

  • New plants grow from nodes along stems, and broken stem fragments can float away and take root in mud.
  • Fragments can be moved by flowing water, machinery and boats.
  • Plants mostly spread at the end of the growing season when nutrient levels are low; there is no evidence they have produced fruit or seed in Australia.

Control options

  • Remove individual plants and small infestations by hand, taking all plant parts from the soil and water body.
  • Check regularly and remove regrowth until plants stop re-growing; excavators can be used for large infestations.
  • Larger infestations can be treated with registered herbicides approved for aquatic use, following product labels and permits.
  • Dispose of plant parts appropriately and contact your local council for disposal advice.

Hygiene and washdown

  • Before leaving a waterway, check and remove plant material from boats, canoes, trailers, vehicles, machinery and fishing gear, and clean machinery before moving it off site.
  • Avoid running boat motors or paddling through water plants, and never dump unwanted water plants.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 4 of 11 regions. Regional priority weed in Greater Sydney, Murray, Riverina, South East. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Check NT list. There is no NT weed profile for it. Check the NT declared weeds list for its current status.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria

Sources