Montague Island is one of the main grey nurse shark aggregation sites on the NSW South Coast. The Marine Life Network lists Shark Gutters on the northern side of the island at 25–35 m, describing rocky gutters with up to half a dozen grey nurse sharks, alongside several deeper sites. Underwater Safaris runs dedicated grey nurse dives at 14–26 m from November to April and requires Open Water certification. Narooma Charters notes that grey nurse sharks take up residence in the warmer months, from February.

Grey nurse sharks are critically endangered on Australia's east coast. They gather in gutters and caves at a limited number of sites, hovering almost motionless in the current, and are docile if divers behave well. The gutters are rocky channels between reef ridges with sand or gravel floors; the sharks cruise slowly along them, often turning back past divers waiting at the edge. The surrounding reef has kelp in the shallows and sponges and gorgonians deeper, with schools of yellowtail, silver sweep and one-spot pullers, blue groper, red morwong and kingfish. Seals frequently cruise through from the nearby colony.

The dive suits Open Water divers who follow the grey nurse code of conduct, though depth and current mean Advanced certification is an advantage. Montague is grey nurse shark critical habitat, with special rules for fishing and diving. The position of the gutters has not been published and operators prefer to keep it that way; dive with a Narooma operator who will brief on behaviour. Combined with a seal dive, this makes a memorable day.

Boat access only. Narooma Charters leaves from the Narooma town wharf on Wagonga Inlet (about 25 minutes to the island) and Underwater Safaris from Narooma marina; private boats launch at the Apex Park or Bar Beach ramps inside the inlet. Every trip crosses the Narooma bar, one of the most dangerous on the NSW coast, so departures depend on bar conditions; Bermagui harbour (about 24 km by sea) is the fallback launch point.

The grey nurse gutters are on the northern side of the island. Operators anchor or drop divers up-current of the gutters so they can settle quietly at the edge.

Montague Island is about 9 km offshore and fully exposed, but operators can usually find a sheltered side. The main limit is the Narooma bar, which closes in moderate easterly or southerly swell, especially on a run-out tide, so trips are often delayed or cancelled. Currents are strongest around the northern and eastern sides.

The northern side is exposed to current and to southerly swell wrapping around the island; operators pick calm, low-current days for the shark dive.

Descend to the edge of the gutters at 14–20 m, settle low and still beside the rock and let the sharks swim past. Do not enter the gutter or chase. After the shark encounter, move along the reef shallower and ascend on the line or an SMB.

Underwater Safaris runs grey nurse shark dives November–April (14–26 m, Open Water certification required); Narooma Charters notes grey nurse residence from February. The Marine Life Network lists Shark Gutters at 25–35 m.