Ninepin Point Marine Nature Reserve lies at the mouth of the Huon River on the western shore of the D'Entrecasteaux Channel, and it protects one of the most unusual reef communities in Australia. It was among Tasmania's first four marine reserves, declared in September 1991, and was later expanded; fishing and collecting are prohibited. The key to its ecology is the Huon River.

Tannin-stained fresh water flows out over the denser seawater, forming a dark surface layer that filters out much of the light. As a result, animals that elsewhere live only in deep water – sea whips, sea pens, delicate sponges, lace bryozoans and other filter feeders – grow on reefs just 5-15 m deep. The Marine Life Network guide describes an extensive reef system stretching about 100 m from shore in 6-9 m, with kelp gardens and fish including bearded rock cod, weedfish, pipefish and leatherjackets, and notes that the tannic water brings deep-water species into the shallows.

Go Dive Tasmania lists it at 3-10 m for all certified divers and notes protected macro life. Weedy seadragons and seahorses are found in the kelp. The Parks and Wildlife Service recommends scuba for the best experience but notes that snorkellers can see rockpool life and diverse flora in summer and autumn.

Divers need a good torch even on sunny days, because the water beneath the tannin layer is dim and green-brown. The site suits patient divers interested in invertebrates and macro photography. Respect the no-take rules, keep fins off the fragile sessile life and avoid stirring the fine sediment.

From Hobart drive to Huonville then take the Channel Highway (B68) via Cygnet towards Verona Sands, or come down the Channel Highway through Kettering and Gordon (about 1 hour 15 minutes, 70 km). The reserve is signposted off the road near Verona Sands. The Marine Life Network guide notes a fairly short walk down to the shore, or divers can request a gate key from the Parks and Wildlife Service to drive closer.

Carry gear down the track to the rock platform and enter where the reef system begins; the reefs stretch about 100 m from shore.

The Huon River mouth and lower D'Entrecasteaux Channel are sheltered from ocean swell by Bruny Island, but northerly and southerly winds funnel along the channel and raise a steep chop. The dominant influence is the Huon River: its tannin-stained, fresher water forms a dark surface layer that cuts light, especially after rain, when visibility can drop to 1-3 m. After dry spells visibility may reach 8-10 m beneath the tannin layer.

Tidal currents are mostly mild. Late summer and autumn, after dry weather, are best; the area can be dived year-round. Parks notes summer and autumn as the best snorkelling seasons.

Enter from the rock platform, swim out over the kelp to the reef edge at 6-9 m, and explore slowly with a torch – the tannin layer makes it dim even at shallow depth. Look for sea whips, sponges and bryozoans that normally live much deeper. Return along the reef.

Go Dive Tasmania – lists Ninepin Point Marine Reserve as a shore site (3-10 m, all certified divers); Underwater Adventures Tasmania – Channel trips; Hobart clubs.