Marmion Marine Park, declared in 1987 as Western Australia's first marine park, stretches about 20 km from Trigg Island to Burns Beach and protects more than 136 fish species, ten seagrass species and 21 seabird species. Whitfords Rock is one of the inshore reefs that DBCA lists as boat-access dive sites in the park, together with Wreck Rock, Cow Rocks, Wanneroo Reef and the Centaur wreck. The park guide describes these inshore reefs as having intricate overhangs, ledges, caves and swim-throughs.

The reef is limestone surrounded by sand and seagrass, typical of the Whitfords–Mullaloo coast. Expect buffalo bream, wrasse, scalyfin, western blue devils, herring cale, old wives and leatherjackets, with lobsters and Port Jackson sharks under the ledges and sponges and small corals on the walls. Australian sea lions and dolphins move through the park.

Wreck Rock, listed separately by DBCA, lies in the same inshore reef system; no detailed published guide to either site was found, so this record covers both until better information is available.

The reefs suit Open Water divers with their own boats who want to explore the quieter northern part of the park. Depth and position details should be obtained from the sounder or from local operators.

The site is lightly dived compared with Boyinaboat and the MAAC trail, which means fish are relatively approachable, but it also means there is little recent information on conditions. Carry a surface marker buoy and check the zoning map before fishing. Water is coolest (about 17 °C) in late winter.

Launch at Hillarys Boat Harbour (public ramps off Southside Drive) or the Ocean Reef boat ramp further north. Whitfords Rock lies off the Whitfords–Mullaloo coast, a short run north of Hillarys (about 10 minutes) or south from Ocean Reef. Anchor in sand beside the reef, keeping clear of sanctuary zone buoys.

Hillarys Boat Harbour has parking, toilets, fuel and dive shops, and it is about 25 minutes from the Perth CBD via the Mitchell Freeway and Hepburn Avenue.

Marmion's reefs are exposed to south-westerly and westerly ocean swell and to the afternoon south-westerly sea breeze (the Fremantle Doctor), which in summer usually arrives between late morning and early afternoon. Dive in swell under about 1.5 m and light easterly winds, early in the day. Visibility drops after westerly swell and winter storms.

Anchor in sand, explore the reef edges and overhangs around the rock and return to the anchor.

Occasionally included on Marmion boat dives; mostly private boats.