Environmental Research

Can Seaweed Help Clean Up Polluted Waterways?
Waihou River Pilot Study.

A pioneering pilot project with the University of Waikato tested whether native sea lettuce could naturally remove nitrogen and phosphorus from river water — achieving up to 90% nitrogen removal and 80% phosphorus removal.

University of WaikatoWaihou River2022-2024Ulva australis
90%
Nitrogen Removal
80%
Phosphorus Removal
6–10 kg
Seaweed Harvested per Week

Rivers and estuaries face a serious challenge: nitrogen and phosphorus runoff from farmland is overwhelming waterways, degrading water quality, and threatening aquatic ecosystems. AgriSea was proud to be part of a pioneering pilot project testing whether seaweed could provide a natural, sustainable solution.

In partnership with the University of Waikato, a purpose-built facility was established at the Kopu Marine Precinct, adjoining the Waihou River estuary. Three land-based tanks were stocked with native Ulva australis (sea lettuce) to treat river water. Weekly re-spawning with 300g of sea lettuce spores resulted in harvesting an impressive 6kg to 10kg per pond, per week. But what was more astounding was that the sea lettuce absorbed up to 90% of nitrogen from the river water, along with 80% of phosphorus plus heavy metals. This water can then be released back into the environment, cleaner and safer than before.

Seaweed collection at the beach

Harvesting native seaweed for bioremediation research

A Collaborative Effort

The project was made possible through a collaboration of partners, including the Ministry for Primary Industries, AGMARDT, Te Waka Anga Whakamua Waikato, Veolia, Thames-Coromandel District Council, Hauraki District Council, Ngāti Maru, Ngāti Hako, and PWC. Funding contributions came from MPI, AGMARDT, and AgriSea, with the local councils providing land and support for consents.

A First for New Zealand

This pilot marks the first time diffuse-source nutrient runoff has been treated using a seaweed-based bioremediation system in New Zealand. Beyond cleaning the water, the project demonstrated how nutrient-rich biomass can be easily grown and perhaps one day transformed into value-added products, supporting a bio-circular economy.

Looking Forward

The trial is now complete, and the results highlight the enormous potential for scalable seaweed-based solutions to protect waterways, support coastal ecosystems, and create sustainable products. AgriSea is keen to keep exploring scalable solutions like this one, so watch this space.

Interested in learning more about our research?

Explore our other research initiatives and discover how AgriSea is pushing the boundaries of seaweed science for sustainable solutions.

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