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. DBCA's guide lists The Lumps among the inshore reefs, with Boyinaboat Reef, Cow Rocks, Wanneroo Reef, Wreck Rock, Whitfords Rock and Burns Rock, that attract divers with intricate overhangs, ledges, caves and swim-throughs. SSI's Perth guide names North Lump as one of the park's dive features, with blue groper, crayfish, Port Jackson sharks and corals.

The Lumps are limestone bommies and reef patches rising from sand and seagrass. Their tops are covered in kelp and algae, and their sides are undercut into ledges and small caves that shelter western rock lobster, Port Jackson sharks (especially in winter and spring), wobbegongs and buffalo bream. Wrasse, scalyfin, western blue devils, old wives, morwong and bullseyes are common, along with sponges and small corals.

The inshore position makes the reefs a short boat ride from Hillarys and gives them some protection from the swell, but visibility is usually lower than at Three Mile Reef and Little Island.

The site suits Open Water divers and is a good choice for an easy boat dive or a second dive. Depths and positions have not been published in detail, so this record relies on the park guide and general descriptions of Marmion's inshore reefs; ask the operator or check the sounder.

As with all of Marmion's reefs, check sanctuary zone boundaries before fishing, and do not take lobsters from sanctuary areas.

Launch at Hillarys Boat Harbour (public ramps off Southside Drive) or the Ocean Reef boat ramp further north. The Lumps are among the inshore reefs a short run (5–10 minutes) north-west of the harbour entrance. Anchor in sand beside the reef, keeping clear of sanctuary zone buoys where anchoring rules apply.

Image Dive & Charters includes Marmion's inshore reefs on its weekend morning charters from Southside Drive.

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. The inshore reefs get some protection from the outer reef lines, but swell over about 1.5 m still produces surge and poor visibility. Dive early in the day in light easterly winds.

Visibility is excellent in summer when the swell drops.

Anchor in sand next to a lump, circle its base, check the overhangs and swim-throughs, then move to the next bommie if they are close together, returning to the anchor with air to spare.

Image Dive & Charters and other Perth operators include Marmion's inshore reefs on weekend boat dives; private boats.