Rocky Bay is a Swan River dive on the North Fremantle side of the river, below the limestone cliffs near Rule Street. The bottom slopes sharply from the entry: the river drops to 5–6 m almost immediately and reaches 8.5 m in the channel, with a shallow sand bar on the far side. Howies notes that it is generally a poor dive, worth doing mainly when the ocean is too rough.

The riverbed near shore is rocky, with a line of rocks along the bank where metal debris, a push bike and the obligatory tyre have collected. Across the channel the sand bar is shallow. Marine life includes schools of toadfish, many sea stars, crabs, seahorses, nudibranchs, horseshoe worms and scattered tube worms on the bottom.

Divingwawrecks lists two wrecks on the southern shoreline of Rocky Bay, the Mayfield and the City of Perth, but warns that access is difficult because of the cliffs and currents.

The river here is heavily used by ferries, recreational boats and jet skis, so divers must use a flag and stay near the bank. Visibility is usually murky and full of weed.

Rocky Bay suits experienced local divers who want a short river dive near Fremantle on a stormy day. For a better river experience, Bicton Baths and the Coombe are nearby.

River temperatures swing more than the ocean: about 22–26 °C in late summer but as low as 13–15 °C in winter, when a 7 mm suit or drysuit makes a long dive more comfortable. Rinse gear well afterwards, as the estuary water is often high in organic matter.

From Stirling Highway in North Fremantle turn onto Harvest Road, then left into Rule Street, and pull into the car park on the right above the dive site to kit up. A set of uneven steps leads down to a small beach; take care. An easier alternative entry is next to the River Police at the bottom of Harvest Road, with two small sets of steps, a wall and a small jetty.

About 5 minutes from Fremantle.

Unaffected by ocean swell, which makes it an option only when the coast is closed. Slight current in the middle of the channel produces a slow drift on the incoming tide; dive near slack water. Visibility is generally poor, murky and full of weed, and it worsens after rain and with boat wash.

Enter from the beach, descend the steep slope to 5–6 m and head south-east towards the boating channel, or cross the channel at about 6.5 m towards the shallow sand bar. Stay close to the rock line on the return and ascend near the bank.

No operator; dived independently when the ocean is rough.