Home Postcodes by state WA 6173 Postcode 6173 6173 is the postcode for Secret Harbour, WA. Localities with postcode 6173Secret HarbourWA Postcode 6173 State or territory Western Australia (WA) Localities 1 Council area Rockingham Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 6172 · Postcode 6174