[3] In the fiords, heavy rainfall runs off from the surrounding mountains creates a permanent freshwater layer to about 5 centimetres (2.0 in) to 10 metres (33 ft) below the surface.

A layer of calm, clear and warm seawater provides a habitat for a range of sponges, corals and fish to about 40 metres (130 ft) below the surface.

A final layer of seawater, too darkened by tannins from vegetation run-off to support most marine life, extends to depths of up to 400 metres (1,300 ft).

[1] The main deep basin has steep rock wall and no exposure to the open ocean swell, with a moderate to thin freshwater layer, and a large amount of shading from nearby mountains, providing a habitat for the highest density of black coral in Fiordland.

[12] The reserve was part of a conservation strategy the Fiordland Marine Guardians launched in 2002 and presented to the Ministry for the Environment Marian Hobbs and Minister of Fisheries Pete Hodgson in 2003.

However, members of Ngāi Tahu may remove pounamu provided they have the right authorisation, only collect by hand, keep disturbance to the site to a minimum, and only carry as much as they can in one trip.