One of the major attractions of Abel Tasman National Park, Tonga Island Marine Reserve includes sandy beaches, boulder headlands, rocky reefs and small estuaries. The reserve is named for Tonga Island, which is offshore from Onetahuti Beach.Foot access to the reserve is along the coast track from north or south. The nearest carpark is at Awaroa. Allow a full day for the return trip, because it’s only safe to cross Awaroa Inlet two hours either side of low tide.In summer and autumn, the best snorkelling is around the rocks between Tonga Quarry and Foul Point. Scuba divers should target reef systems in the north of the reserve, at about 15 metres depth.The underwater environment is notable for the attractive film of pink algae that coats much of the rock and the abundance of grazing animals, such as kina and turban shells. Caves and crevices on the reefs may conceal a crayfish passing the day in secret or a conger eel lurking in the dim light. A torch will illuminate a colourful array of animals encrusting the rock surfaces. Look out for the more common inshore fish - wrasse, blue cod, snapper, tarakihi and moki.At any time of the year, sea kayaking is a great way to explore the reserve. Sea-kayakers can discover Mosquito Bay and Shag Harbour - beautiful coves that the walking track doesn’t reach. From a kayak you could also encounter dolphins and penguins. Seals are common around Tonga Island, especially during winter when they travel north on their annual migration.If you’re on foot, the small estuary behind Onetahuti beach is a good place to see herons, oyster catchers and other wading birds. At the southern end of the beach the track climbs around a small headland to Tonga Quarry, where granite was quarried early this century. Continue down the coast to the beautiful arches at Arch Point. There is a good variety of seaweeds here, visible at low water. There are also rock pools to investigate.