A long-running shellfish reef trial in the Pine River catchment near Bridgeman Downs is demonstrating measurable nutrient reduction, providing new insights into how nature-based systems can support cleaner waterways.
Background on the Pine River Trial
Unitywater began the shellfish reef project in the Pine River nearly two years ago to assess whether oyster-based reefs could reduce nutrients downstream of the Murrumba Downs Wastewater Treatment Plant. The initiative, delivered with UniSC, OzFish and Healthy Land and Water, forms part of a broader commitment to improve waterways across the region.
The approach tests how recycled oyster shells can be used to support live shellfish, building small reef structures capable of filtering water as they grow. The trial sits within the Pine River catchment, which includes the Albany Creek and Bridgeman Downs area.
How the Reef System Works
Each reef consists of baskets made by OzFish volunteers and filled with around 18 kilograms of recycled oyster shells. The shells are sun-cured for 12 months to remove impurities and then prepared for oyster spat before installation.
Researchers measure performance by analysing nitrogen in shellfish tissue, nitrogen deposited into surrounding sediment and reductions in the water column. In the first six months of results, monitoring showed a reduction of 7.24 kilograms of nitrogen.
Unitywater’s modelling indicates that approximately 154 reefs, covering an area similar to two rugby league fields and containing about 6,500 baskets, could offset nitrogen discharged from a treatment plant servicing around 10,000 people.
Ecological Findings So Far
UniSC research teams reported that more than 95 per cent of shellfish reefs nationwide have disappeared, making restoration work significant for water quality and ecological recovery. Findings from the Pine River show the reefs are effectively storing nutrients within the living shellfish and the reef structure.
Researchers used multiple techniques, including nitrogen testing in shellfish flesh and surrounding sediment, to understand how nutrients settle and transform within the system.
Expansion of the Trial
Following development approval from the State Assessment Referral Agency, Unitywater will add two more reefs to the North Pine River between Lawnton and Murrumba Downs. These sites will test how different depths, salinity levels and flow conditions influence nutrient removal.
Unitywater’s Environmental Sustainability Plan outlines a wider commitment to divert or offset nutrients from waterways by 2040. The shellfish trial forms part of this broader program, which includes wetland restoration, nutrient offset projects and recycled water schemes.
Relevance to Bridgeman Downs
Bridgeman Downs is located within the Pine River catchment, meaning improvements in water quality upstream contribute to healthier waterways for suburbs connected to this system. The trial’s findings offer data that may guide future restoration activities benefiting the wider northern Brisbane region.
Next Steps
Further monitoring will assess long-term nutrient storage, reef growth and performance in varied conditions. These results will support decisions on whether nature-based systems can be deployed more widely alongside existing wastewater treatment processes.
Published 3-Nov-2025
