The marine reserve at Wet Jacket Arm, Moana Uta, covers the entire sound between Entry Island and the head of the sound. The reserve was one of eight established in 2005 as part of the management measures proposed by the Guardians of Fiordland, and covers about 2,007 hectares.
The reserve includes significant expanses of rock wall, broken rocky reef, deep basin and estuarine habitat. Subtidal rocky reefs around Entry Island have dense beds of kelp and very low kina populations. Rock walls near Oke Island receive a significant amount of tidal flow and have correspondingly high densities of lampshells (brachiopods) and other suspension feeders.
The basin is characterised by steep rock wall habitats and a deep basin with no exposure to the open ocean swell, a moderate to thin freshwater layer and a large amount of shading from the mountains above, particularly near the head of the fiord. These factors combine to produce the highest known density of black coral at any sites in the fiords.