Ruataniwha Inlet is a moderate-sized (863ha) shallow tidal lagoon estuary that has a broad entrance mouth. It is located at the delta of the Aorere River. Large barrier spits project southward creating a relatively stable area in the north of the inlet. About 48 hectares of saltmarsh and intertidal habitat has been lost through conversion to pasture.
Ruataniwha estuary is valued for its aesthetic appeal, its rich biodiversity, shellfish gathering, swimming, duck shooting, fishing, boating, walking and scientific appeal. A small port is located at the northern entrance.