The Northland medical officer of health is calling on the community to do more to protect traditional kaimoana collection sites.
Dr Jonathan Jarman says sewage, stormwater, septic tank and farm runoff flow into the region's harbours every time it rains heavily, shutting down beaches and shellfish collection for up to a month at a time.
He says more than 16 million litres of sewage overflowed into the Whangarei Harbour in the recent rainfall.
Dr Jarman says the community seems to struggle to respond appropriately.
He says iwi, district and regional councils, the health board, the department of conservation and community members need to work together to upgrade pipeworks and reticulation systems.