Withnell Bay is one of two self-guided shore dives promoted by Pilbara Dive and Tours. It lies on the south-western edge of Murujuga National Park, about 25 minutes from Karratha. The bottom is sand with small corals and weedy patches, reaching 5–6 m at high tide.

Anemones, small rays, nudibranchs, tropical fish, turtles and larger rays are regular sightings. Visibility is under 5 m in the warmer months and up to 10 m in the cooler months. It is best dived at slack high tide.

About the Dampier Archipelago: the archipelago's 42 islands off Dampier and Karratha hold one of the most diverse marine environments in Western Australia, with more than 650 recorded fish species, coral reefs, sponge gardens and seagrass meadows — all set against red Pilbara rock and the world's largest concentration of Aboriginal rock art on the Burrup Peninsula (Murujuga). It is heavily fished and boated by locals but lightly dived, and visiting divers usually go with Pilbara Dive and Tours or a local club. The combination of big tides, turbid inshore water and strong currents means the outer islands generally offer the best visibility and coral, and dive timing is planned around slack water.

Planning notes: Open Water certification is recommended and the site is rated beginner. Expect to spend most of the dive around 4 m, with a maximum of about 6 m. It is a shore-access site that can be visited independently when conditions suit. Currents are significant, so timing around the tide is part of the plan. Best season: April–October (outside cyclone season; best visibility in cooler months). Traffic: moderate (occasional charters/club dives).

From Karratha drive about 25 minutes towards Dampier and the Burrup Peninsula, take Withnell Bay Road and turn left at the end onto a dirt track (4WD or AWD recommended). Park near the beach and enter from the sand. Dive at slack high tide; snorkel at low tide.

Display a dive flag — weekend boat traffic from the Withnell Bay ramp is heavy.

The Dampier Archipelago is sheltered from ocean swell by its islands, but the big Pilbara tides (spring ranges approaching 5 m) drive strong currents between the islands and control visibility; dive near slack water and plan around neap tides for the clearest water. Visibility is usually under 5 m in summer and up to 10–15 m in the cooler months, better at the outer islands. Strong easterly winds in winter and afternoon sea breezes chop up the crossings.

Cyclone season runs November–April and the Pilbara coast is Australia's most cyclone-prone; charters stop during warnings. Irukandji and box jellyfish can occur in the warmer months. Water temperature ranges from about 21 °C in July–August to 30 °C in January–February.

Enter at slack high tide, swim out over the sand to the small coral and weed patches at 4–6 m, and navigate a simple out-and-back along the bay with a flag, returning before the tide turns.

Self-guided; Pilbara Dive and Tours (Karratha) provides gear hire, fills and site briefings ('Self Guide Dive and Snorkel').