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Protecting oyster productivity through evidence-based decision making

Oyster lease in the Merimbula Lake

The ºÚÁÏÍø´óÊÂ¼Ç Water Research Laboratory, in partnership with the Department of Primary Industries and Regional Development (DPRID) NSW Shellfish Program, led a large study to support evidence-based decision making on the closure of productive oyster harvest areas following sewage overflow events in NSW.Ìý

Oyster harvest areas that are exposed to human sewage are closed for a mandatory 21 days to protect consumer health, and this study aims to provide high quality and accessible information to the NSW Shellfish Program to ensure decisions about closures are supported by quantitative information. The project covered 11 estuaries in NSW, from the Tweed River in the north to Pambula Lake in the south, which together account for over 80% of commercial oyster production. Many of these locations faced substantial closures during the extensive storm and flood events in the last five years.
Project Engineer Yarran Doherty completing fieldwork in Wagonga Inlet

Practical tools for future decision making

Sewage overflows into estuaries occur under a range of conditions, often due to malfunctioning or overwhelmed infrastructure. As a result, the environmental conditions—such as river inflow or timing of the tide—at the time of an overflow can vary significantly. While experimental data like large-scale dye release experiments can help understand pollutant transport under specific conditions, it is impractical to replicate this across all possible scenarios. To address this, the study combined numerical modelling with site-specific field investigations, offering a cost-effective and scalable approach to understanding pollutant transport across diverse estuarine environments.
Dye experiment in the Pambula Lake

The study involved over 35 dye experiments across NSW to understand mixing dynamics in various estuaries. This data was used to develop and validate detailed numerical models that simulate water movement and pollutant dispersion over multiple days and weeks. Thousands of ‘what-if’ scenarios were tested to assess the risk to oyster harvest areas under different overflow and environmental conditions. The results were compiled into a purpose-built decision support tool, enabling rapid access to model outputs during future overflow events. This tool empowers the NSW Shellfish Program to make informed decisions, supports targeted closures, and provides confidence to the oyster industry that actions taken are necessary and protective of both public health and industry reputation.