Arthur Bay is one of the small, scenic bays on the Radical Bay Road on Magnetic Island's north-east coast, below the Forts walk, and one of the most photographed spots on the island. The North Queensland Underwater Explorers Club groups it with Florence Bay as an area of fringing reef patches at about 7 m, with brain, staghorn and lettuce hard corals, and the Marine Life Network lists it for snorkelling at 2–10 m with swim-throughs, caverns, bommies and coral. The best coral and snorkelling are on the shallow left-hand (northern) side of the bay, where the fringing reef meets granite boulders.

Here the boulders form small caverns and swim-throughs, and coral heads rise from the sand. Turtles are common, feeding on algae and resting under ledges, and the usual island reef fish – parrotfish, damsels, wrasse, rabbitfish, butterflyfish and small groupers – are plentiful. Continuing past the point leads to the rocky cove with the old dredge boilers.

The bay's weak points are seasonal. In the hot months sargassum blooms can blanket the shallow reef, and the club recommends visiting in winter when the macro-algae die off. The access road is notoriously rough, and on calm days the bay can be crowded with snorkellers and boats, so early morning or late afternoon visits are best.

For snorkellers and new divers it is a rewarding shore dive in a beautiful setting, and one of the easier places on the island to find turtles. It is part of the Marine National Park green zone.

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. From Horseshoe Bay, take Radical Bay Road, which leaves the main road near the Forts walking-track car park.

The road is unsealed, prone to deep wash-outs and in a 'constant state of poor repair' (NQUEC); many hire-car and moke agreements exclude it, so check first or go by boat from the Horseshoe Bay ramp (10–15 minutes). From the small Arthur Bay car park a short, steep track leads down to the beach – a carry of 100–200 m.

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. NQUEC advises visiting in winter when the macro-algae die off; best early morning or late afternoon.

Enter from the beach and head to the left (northern) side, where coral cover is best, working along the fringing reef and bommies at 3–8 m; confident divers can continue to the dredge boilers in the rocky cove beyond. Return along the shoreline.

No regular operator; independent divers and snorkellers, NQUEC club dives. Nearest dive centres for gear hire, fills and local advice: Pleasure Divers Magnetic Island, Adrenalin Snorkel & Dive.