Seawater desalination plants can interact with marine ecosystems, requiring robust baseline datasets to support post‑commissioning monitoring. The Belmont Seawater Desalination Plant, located in Lake Macquarie (NSW), is currently under construction. Once operational, the plant will draw seawater via a new ocean intake, treat it using reverse osmosis to produce potable water, and discharge commingled brine and wastewater through the existing Belmont Wastewater Treatment Works offshore outfall.
The pre‑commissioning fish ecology assessment formed part of a broader suite of ecological baseline studies and aimed to characterise fish assemblages at intake, outfall, and reference locations. Fish communities were surveyed using Baited Remote Underwater Video Systems (BRUVS), Underwater Visual Census (UVC), and Environmental DNA (eDNA) across four seasonal sampling events between 2023 and 2025.
Results demonstrated spatial and temporal variability in fish assemblages, with natural rocky reef reference sites generally supporting higher abundance and diversity compared to the outfall pipeline (artificial reef habitat) and the sandy seabed of the proposed intake location. Temporal variability was most clearly reflected in eDNA results, while UVC surveys were largely constrained by underwater visibility.
Overall, the integrated application of BRUVS, UVC, and eDNA provided complementary datasets and a robust baseline suitable for comparison with post‑commissioning monitoring under a multiple‑before‑after‑control‑impact (mBACI) framework.