Uwhi Harakeke Weed Mats

Location: Te Arawa Lakes, Rotorua, Aotearoa New Zealand
Project type: Freshwater ecosystem restoration / invasive aquatic weed management
Delivery/lead organisations: Te Arawa Lakes Trust in partnership with Te Roopu Raranga Ki Rotorua (weavers) and Toitū Te Whenua – Land Information New Zealand (funder)
Date/period: Trials initiated 2020–2021; installations continuing
Scale: Lakebed ecosystem restoration sites
Primary system or theme: Freshwater restoration; mātauranga Māori; nature-based invasive species management

Context

Why this site matters
Freshwater lakes across Aotearoa New Zealand have been increasingly affected by invasive aquatic plants that alter ecosystem structure and threaten Indigenous biodiversity. In the Te Arawa Lakes catchment, invasive species such as hornwort (Ceratophyllum demersum) form dense underwater beds that outcompete native aquatic plants and disrupt ecological processes. 1,2 In response, Te Arawa Lakes Trust and mana whenua have explored restoration approaches informed by mātauranga Māori, integrating Indigenous ecological knowledge with contemporary environmental management. 3 One such approach involves the revival of uwhi: woven mats made from harakeke (Phormium tenax) that are placed on the lakebed to suppress invasive aquatic weeds. 2

Challenge or constraint

What wasn’t working/what needed to change
Invasive aquatic weeds present a persistent challenge for lake restoration. Mechanical removal methods can be costly and temporary, as plant fragments can easily regrow. Chemical control methods may also have ecological limitations and may not align with community aspirations for restoration approaches that reflect cultural values and kaitiakitanga. 1 Restoration practitioners sought methods capable of supporting long-term ecological recovery, including enabling the re-establishment of native aquatic plants.

Intervention

What was done
The restoration approach involved reviving the traditional practice of uwhi by weaving mats from harakeke and placing them on the lakebed in areas dominated by invasive weeds. The mats block sunlight from reaching plants beneath them and physically restrict growth, suppressing invasive weeds and creating conditions for native aquatic species to recolonise as the mats degrade. 2

Key components

  • Large woven mats made from harakeke
  • Community-led weaving processes drawing on traditional techniques
  • Placement of mats directly onto the lakebed over invasive weed beds
  • Use of natural fibres that gradually biodegrade in water, avoiding the need for later removal
  • Collaboration between restoration practitioners, mana whenua, and local communities

Implementation notes

Design and delivery considerations

  • Effective weed suppression requires mats sufficiently dense to block sunlight and remain stable on the lakebed
  • Weights or anchors may be used to ensure mats remain in position in areas with water movement
  • Site selection should target areas where invasive weeds are well established but where conditions may support native vegetation recovery once competition is reduced
  • The weaving process enables community participation and cultural knowledge transfer alongside restoration work 3
  • Because mats gradually biodegrade, they function as a temporary suppression layer and may require periodic reinstallation depending on site conditions

Outcomes

Observed or reported outcomes

  • Trial installations in the Te Arawa Lakes showed that uwhi mats were able to suppress invasive aquatic weeds beneath them after approximately twelve months 2
  • Lakebed areas beneath the mats became more suitable for the re-establishment of native aquatic vegetation following weed suppression 7
  • Strong community engagement documented through weaving and installation activities 7

What is plausible but unmeasured

  • Improved biodiversity through native aquatic plant regeneration over longer timeframes
  • Reduced reliance on chemical weed control methods
  • Strengthened cultural relationships with freshwater ecosystems through knowledge transmission

Evidence and limits

What the evidence supports
Reports from Te Arawa Lakes Trust suggest that uwhi can effectively suppress invasive aquatic weeds and support conditions for native lakebed ecosystem restoration. 1,2

Key limitations or uncertainties

  • Most evidence comes from pilot projects and restoration reports rather than long-term ecological studies
  • Performance may vary depending on water depth, sediment conditions, and the species composition of invasive weeds present
  • The approach may be most suitable where invasive plants dominate shallow lakebeds, mana whenua collaboration is possible, and communities have access to harakeke and weaving expertise

Relevance to design practice

  • Ecological restoration can integrate mātauranga Māori with biodegradable natural materials to address environmental challenges while supporting cultural continuity 3
  • Uwhi is a site-specific ecological intervention rather than a universal weed management solution; its effectiveness depends on environmental conditions and ongoing restoration planning
  • If you are interested in integrating uwhi into a project, contact Te Arawa Lakes Trust to learn more about the techniques and mātauranga involved

References

  1. RNZ. (2021). Te Arawa Lakes Trust utilising mātauranga Māori to combat invasive weeds. rnz.co.nz
  2. Te Arawa Lakes Trust. (2022). Uwhi. tearawa.io
  3. Clapcott, J., Ataria, J., Hepburn, C., Hikuroa, D., Jackson, A. M., Kirikiri, R., & Williams, E. (2018). Mātauranga Māori: Shaping marine and freshwater futures. New Zealand Journal of Marine and Freshwater Research, 52(4), 457–466.
  4. Nicholls, M. (2004). Cultural perspectives from Aotearoa/New Zealand. Journal of Intergenerational Relationships, 1(4), 25–34.
  5. Quigg, R., Kewene, F., & Morgaine, K. (2023). Initiating decolonization: From The Last Straw! to Whāriki. AlterNative: An International Journal of Indigenous Peoples, 19, 495–498.
  6. Lipscombe, A., & Liew, C. (2025). Affective encounters with digital knowledge collections: Towards supporting Indigenous wellbeing. IFLA Journal.
  7. Te Ao Māori News. (2022). Using traditional uwhi to kill weeds; help plants regenerate. teaonews.co.nz