The Avon Heathcote Estuary/Ihutai is the largest semi-enclosed shallow estuary in Canterbury (Bond et al, 2005) and is largely intertidal, with large intertidal banks that are muddy at the river mouths and gradually change to sand towards the outlet (Estcourt, 1967).
These mudflats and sand flats are home to numerous fauna including crabs, mud snails, cockles, pipis and small marine worms (Bolton-Ritchie, 2013a). The estuary also supports 5–6% of the South Island pied oystercatcher population (Bond et al, 2005; Owen, 1992) and is home to 16 fish species, with the most numerous typically yellow-eyed mullet, common smelt and sand flounder (Woods et al, 2014).
Adult inanga (a whitebait species) also utilise the estuary as a migration route to the river mouths where they spawn amongst tidally-inundated grasses (Taylor & McMurtie, 2004).
Salt marsh areas are present around the margins of the estuary and contain a variety of species including raupo, oioi and sea rush (Estcourt, 1967; Jupp et al, 2007; Owen, 1992).