Green Island is a vegetated coral cay 27 km north-east of Cairns, a national park surrounded by fringing reef and seagrass beds, and the most accessible reef island from the city. It has been a tourist destination for more than a century and now carries a resort, a long jetty, restaurants and a dive operation, so it is far from wilderness, but the reef around it is protected and the diving is easy and reliable. Big Cat Green Island, operated by Reef Unlimited, runs all dives as guided beach entries.

Introductory divers, who need no certification, spend about an hour at an average depth of 5 m at sites the operator calls Fish Cinema and Finding Nemo. Certified divers have three more advanced sites: Pinnacle Canyons, a series of coral heads reaching 17 m; Reef Edge Drift, along the outer margin at 15 m; and Northern Drift, to 21 m. Marine life includes colourful reef fish, giant clams, clownfish, turtles, blacktip reef sharks and bull rays.

Green turtles are common, grazing on the seagrass close to the beach, and the seagrass beds occasionally host a dugong. Visibility is the main limitation: being close to the mainland, the water is often 5-10 m and less after rain, so the island suits introductory divers, families, snorkellers and people short on time better than experienced divers expecting outer-reef clarity. Great Adventures also offers diving at Green Island.

Pinnacle Reef, a private Ocean Free mooring about 1 km offshore, has its own entry. The ferries' frequent timetable means divers can choose between a half-day and a full day on the island.

Green Island is 27 km north-east of Cairns, about 45-50 minutes by fast catamaran from the Reef Fleet Terminal (1 Spence Street). Big Cat Green Island Reef Cruises and Great Adventures run several ferries a day, and there is paid parking near the terminal and hotel transfers from most accommodation. Ferries berth at the island's long jetty; walk ashore to the dive shop near the beach, where gear is fitted.

All dives are guided beach entries into shallow, sheltered water, so there is no boat dive; certified divers may be taken further along the reef edge on drift sites. Green Island Resort guests can dive on the day they stay.

The prevailing south-east trade winds (typically 15-25 knots from April to September) are what limit Cairns outer-reef diving: above about 25 knots trips may be cancelled, and exposed eastern moorings are used only in light winds. Summer northerlies are gentler but make north-facing moorings choppy. Box jellyfish and Irukandji are present from about November to May (stinger suits on every dive), and the cyclone season runs November to April, when a system in the Coral Sea can close the reef for days.

Visibility drops after heavy rain and strong winds; spring is usually calmest and clearest. Being closer to the coast, visibility is lower than on the outer reefs, especially after rain. Green Island's western beach is sheltered in south-easterlies and dives run in most conditions, but strong winds and rain reduce visibility to 5 m or less.

The drift sites are timed to the tide. Stinger suits are provided in the November-May season.

Introductory dives wade in from the beach and follow the instructor over seagrass and coral to about 5 m. Certified divers are guided along the reef edge on Pinnacle Canyons (to 17 m), Reef Edge Drift (15 m) or Northern Drift (21 m), drifting with the tide and exiting on the beach or being collected.

Big Cat Green Island (Reef Unlimited) – daily introductory dives (about 5 m) and certified dives at Pinnacle Canyons (17 m), Reef Edge Drift (15 m) and Northern Drift (21 m); Great Adventures – daily Green Island intro and certified diving