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Yellow waterlily (Nymphaea mexicana)

Yellow waterlily was introduced to Australia as an ornamental plant and has naturalised in parts of NSW. Dense infestations can reduce water quality, displace native plants and restrict waterway use.

Key facts

Type: Weed, aquatic.

Native to: Mexico and the southeastern USA.

Established in: QLD, NSW, VIC, SA, WA.

Other names: water lily, Mexican waterlily.

Identification

  • This perennial water weed grows from an underwater rhizome, which is knobby, vertical and up to 30 cm long and 4 cm thick.
  • Its circular, waxy leaves are usually floating, up to 25 cm across, and have a slit near the stalk and wavy margins.
  • Leaves are green above and green or red underneath; the upper surface sometimes has brown markings.
  • Bright yellow flowers with many petals grow above the water and can be up to 12 cm across.
  • Look-alike: White waterlily (Nymphaea alba) has white, pink, red or orange flowers and leaves without brown marks.
  • Look-alike: Giant waterlily (Nymphaea gigantea) has leaves up to 75 cm across and blue or white flowers; Cape waterlily (Nymphaea capensis) has white, blue or bluish-pink flowers and leaves without wavy edges.

Where it grows

In NSW it has been found in the Central and Northern Tablelands, Greater Sydney, Hunter, North Coast and Riverina regions, growing in still or slow-moving waterways up to 2 m deep and preferring nutrient-rich water.

Why it matters

  • Dense infestations reduce water quality and outcompete native aquatic plants.
  • They reduce habitat for native aquatic animals and increase siltation.
  • They can restrict water flows, increase mosquito breeding habitat and limit access to and recreational use of waterways.

How it spreads

  • Yellow waterlily mostly spreads by plant parts: stolons produce new plants at nodes, which detach when small.
  • Water spreads most small plants, and boats and other recreational equipment can also spread them; birds may spread the plants too.
  • Seeds are rarely found in Australia. If present, they are released into the water after flowers are pollinated above water and fruit forms underwater.

Control options

  • Small infestations can be removed by hand, but remove all plant parts because the plant can regrow from rhizomes.
  • Large infestations can be harvested or excavated, but remaining fragments will regrow, so follow-up removal or other control may be needed.
  • Follow up after initial control by looking for and killing regrowth or new seedlings; combining control methods is usually more successful.

Hygiene and washdown

  • Do not run boat or watercraft motors through weed beds, and remove all plant material from boats, canoes, trailers, vehicles, machinery and fishing gear before leaving waterways.
  • 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 5 of 11 regions. Regional priority weed in Central West, Murray, North West, Northern Tablelands, Riverina. 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: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • 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
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources