Wool in, weeds out!

An innovative and sustainable method is being trialled in Taitokerau to suppress Egeria densa an invasive oxygen weed found in Rotokawau on the Poutō Peninsula.

The Northland Regional Council’s Biodiversity, Biosecurity Marine, and Maritime teams collaborated towards the end of 2025 to lay wool matting on 412m square metres of the lake floor with support from local commercial divers.

The New Zealand grown wool which resembles a carpet underlay, offers a non-toxic and cost-effective solution for the NRC.

Northland Regional Council Biodiversity Manager Lisa Forester says until now the lake had been hand-weeded by divers – a process which is painstakingly slow, labour-intensive and costly.

“Using a natural fibre such as wool matting will allow native plants to easily recolonise while acting as a weed suppressant, preventing the oxygen weed from pushing through and hopefully eradicating the pest plant over time.”

Kaipara constituency councillor John Blackwell says ecological monitoring including weed surveillance on dune lakes is part of the Northland Regional Council Biodiversity team’s everyday mahi.

“We are looking forward to the results of this experiment as Rotokawau is one of the 12 lakes ranked as ‘outstanding’ in Te Taitokerau. This particular lake supports threatened underwater plant species and kākahi (freshwater mussels), as well as 14 other threatened species, but is also impacted by the invasive oxygen weed, Egeria densa.”

“If we don’t act now the oxygen weed will eventually fill the lake, smothering native plants in the process and degrading the water quality.”

The Biodiversity team will revisit the lake in late summer to check on the wool matting and continue weed checks twice a year.

With summer underway it is important to use the ‘Check, Clean and Dry’ method when visiting any Te Taitokerau lakes or waterways.

Always check your gear, clean and then fully dry your gear, before moving between waterways.  This is especially important now that the invasive freshwater clam has arrived in New Zealand.