raupō around the water's edge. Sediment is deposited at the river's mouth as a delta. Over time, the arrival of sediment slows, the spit is breached and washed away, the water level lowers, and tides come further inland forming a brackish water ecosystem. During this stage Ōkārito's rimu forest is able to encroach around the edges of the now-lower lagoon, a pattern we can observe today. Flora Ōkārito Lagoon has extensive meadows of eelgrass (Zostera muelleri), one of the few such estuaries remaining in New Zealand; most have been wiped out by pollution and sedimentation after forest clearance. Eelgrass is not a seaweed, but a flowering plant that is pollinated underwater. Eelgrass beds are highly productive, not only drawing nutrients up out of the mud but providing a rich habitat for invertebrates and a nursery for baby fishes. On the inland side of the lagoon are large stretches of saltmarsh and swampland, dominated by jointed wire rush or oioi (Apodasmia similis). This becomes a band of mānuka (Leptospermum scoparium), mingimingi (Coprosma propinqua), and flax (Phormium tenax) shrubland that transitions through kahikatea swamp forest into bush dominated by rimu and silver pine (Manoao colensoi). Ōkārito is one of the few places on the West Coast where the transition of tall rain forest through scrub and rush to brackish water can still be easily observed. The transition zone can stretch quite a distance and contain saltmarsh ribbonwood (Plagianthus divaricatus), cabbage trees (Cordyline australis), and invasive gorse (Ulex europaeus), gradually incorporating kahihatea, southern rātā, and kōwhai (Sophora microphylla) as salinity declines; or it can take place over just a few metres on the bank of a creek. Fauna Over 70 bird species have been reported from Ōkārito Lagoon and the surrounding forest, including 40 species of shorebirds and migratory waders. Paradise shelducks, New Zealand scaup, black swans, and occasional grey ducks can be seen on the water. Black shags (Phalacrocorax carbo), little shags (P. melanoleucos), pied shags (P. varius), and spotted shags (Stictocarbo punctatus) all occur in the lagoon. Caspian terns (Hydroprogne caspia) and white-fronted terns (Sterna striata) are present, and most of the gulls are black-billed gulls (Chroicocephalus bulleri), the world's most threatened gull species. As well as the common white-faced heron, one can see royal spoonbills and the famed white heron or kōtuku (Ardea alba modesta). Banded dotterels and variable oystercatchers breed on Ōkārito Beach. Fernbirds are present all around the