Alma Bay is the heart of shore diving on Magnetic Island: a small, patrolled Surf Life Saving beach in Arcadia with rocky granite headlands at each end, parkland, showers and a dive shop a few minutes' walk away. Pleasure Divers runs its guided shore dives and training here, and describes two distinct dive sites within the one bay – the Coral Gardens and the Canyons on the northern side. The bay floor slopes from sand near the beach to 5–6 m across the mouth, with the remains of an old jetty in about 1.5 m, a small rock wall and a central patch of reef and coral rubble.

The real interest is along the headlands. On the northern point, large granite boulders stack into caves, gullies and swim-throughs that deepen to 8–10 m – the Canyons – with staghorn, plate and brain corals, sea whips and anemones. The Coral Gardens on the northern side have big brain, staghorn and plate corals and colourful soft corals at around 10 m.

Fish and invertebrate life is excellent for a shore dive. Pleasure Divers counts more than 50 nudibranch species here, and the lists include coral trout, six-banded angelfish, unicornfish, honeycomb cod, squirrelfish, sweetlips, bannerfish, Moorish idols, fusilier schools, diamond fish, batfish, goatfish and moray eels. Blue-spotted, shovelnose and cowtail rays lie on the sand, epaulette and wobbegong sharks hide under ledges, painted crayfish sit in the cracks and green turtles are common.

Large snails, cowries and Christmas tree worms reward slow divers. Alma Bay suits beginners and experienced divers alike, and at night the Canyons are a favourite. The bay is a green zone.

Divers regularly find lost sunglasses, masks, weights and knives on the bottom, a sign of its popularity with swimmers.

Magnetic Island is reached by SeaLink passenger ferry from the Breakwater terminal in Townsville to Nelly Bay (about 20 minutes, frequent daily services) or by the vehicle ferry from Ross Street, South Townsville (about 40 minutes). Buses, hire cars and 'topless' mokes run from the Nelly Bay terminal to Arcadia, Horseshoe Bay and Picnic Bay. Alma Bay is in Arcadia, about 5 km from Nelly Bay; buses stop at the Alma Bay lookout on Hayles Avenue.

Park on Hayles Avenue or in the small car park above the beach; a short set of steps and path lead down through the park (BBQs, showers, toilets) to the sand – a carry of about 50 m. Pleasure Divers' shop is a short stroll away. Enter from the sand and swim out along either headland.

Magnetic Island's bays are sheltered from different winds depending on which side they face. The dominant south-east trade winds (15–25 knots, April–September) chop up exposed eastern and southern bays and stir up silt, so the island's best diving comes in the calmer months of August–December and on mornings before the sea breeze. Visibility is usually 3–8 m and occasionally 10–15 m; it drops sharply after strong winds, big spring tides and wet-season rain (January–April) when Ross River and Burdekin run-off discolour the water.

Dive at slack water, ideally high tide. Sargassum seaweed blooms in the hotter months can smother shallow reef flats. Marine stinger season (box jellyfish and Irukandji) runs roughly November to May – wear a full-length stinger suit or wetsuit with hood and gloves, carry vinegar.

Stinger nets are installed at Alma Bay, Picnic Bay and Horseshoe Bay in season. Alma Bay faces north-east and is somewhat protected from the trades, but a fresh south-easterly wraps around and makes the eastern point rough.

NQUEC suggests swimming out along one shoreline, crossing the bay mouth on a compass bearing at 5–6 m, and returning along the opposite shoreline. For the Canyons, follow the northern point where boulders form caves and swim-throughs at 8–10 m; for the Coral Gardens stay on the northern side at 5–10 m.

Pleasure Divers Magnetic Island (Arcadia) – guided shore dives daily at Alma Bay and Geoffrey Bay, PADI courses, gear hire; Adrenalin Snorkel & Dive picks up at Nelly Bay for reef trips.