Whanganui Inlet, also known as Westhaven, is a 13-kilometer-long, 2.5-kilometer-wide drowned river valley running parallel to the northwest coast of New Zealand's South Island. This large, unspoiled estuary is bordered by the lush coastal forest of Kahurangi National Park and is protected as both a marine reserve and a wildlife sanctuary, the first estuary in the country to receive such combined protection. The inlet features extensive tidal sandflats, seagrass beds, and salt marshes that create a rich marine environment, supporting a diverse fishery. It is a remote and scenic destination popular for recreational fishing and boating, offering a unique blend of sheltered waters and access to the Tasman Sea through a narrow channel.