Garden Island forms the western wall of Cockburn Sound: about 10 km long and 1.5 km wide, joined to Point Peron by a causeway and occupied by HMAS Stirling, the Royal Australian Navy's largest base. Because of the base, public access is tightly controlled. The causeway is closed to the public unless entry is sponsored by the military, and visitors by sea are restricted to private boats using moorings and anchorages in designated areas, during daylight hours.

Within these limits the island's sheltered northern and eastern bays are popular with boaters for swimming and snorkelling. The limestone reefs and seagrass around the island support the same life as the rest of the Cockburn Sound margin: buffalo bream, wrasse, sweep, herring cale, cuttlefish, octopus and rays, with dolphins common. The island's western side faces Five Fathom Bank, and offshore reefs such as Challenger Rock lie near its northern tip.

No dive-specific guide to Garden Island was found, and this record exists mainly to document the access restrictions. Divers planning a visit must check the current Defence boating rules, respect prohibited zones around naval facilities, leave before the daylight curfew and keep clear of warships and Defence vessels.

For most divers, the nearby Point Peron, Shoalwater and Five Fathom Bank sites give better and more accessible diving. Garden Island is best treated as a snorkel stop for private boats.

Boats that do visit should carry a copy of the current rules, anchor only in sand, and plan their departure well before the curfew, allowing for the run back across Cockburn Sound against the afternoon sea breeze.

There is no public road access: the causeway from Point Peron is open only to Defence personnel and sponsored visitors. Private boats launch at Point Peron, Rockingham or Woodman Point and use the designated public areas on the island's northern and eastern shores during daylight hours. Obtain current Defence boating rules for Garden Island (prohibited and restricted areas near the naval base, wharves and causeway) before leaving the ramp, and follow buoyed boundaries.

The island's eastern shore is sheltered from south-westerly swell and the summer sea breeze, while the western shore faces the open ocean and Five Fathom Bank and is often rough. Public access is limited to daylight hours, so night diving is not allowed. North-westerly winter fronts make the northern bays uncomfortable.

Anchor or moor in a permitted bay, snorkel or dive the adjacent limestone reef and seagrass edge in 2–8 m, and stay well inside the public area.

No regular dive operator. Private boats visit the permitted bays in daylight.