Mettams Pool is the best-known snorkelling spot on Perth's northern beaches: a lagoon enclosed by limestone reef on West Coast Drive, inside Marmion Marine Park. The inner pools are less than 2 m deep and sheltered enough for children and people with limited mobility, and the main entrance has a ramp. The outer reef, reached through gaps from the lagoon, drops to about 7 m and has swim-throughs, ledges, holes, passages and at least one arch.

The outer reef is surprisingly colourful. Sea fans in yellow, pink, orange, white and red grow in the gutters, along with sponges and sea stars, and Port Jackson sharks shelter in caves in winter. Western blue devils, juvenile buffalo bream, wrasse, scalyfin, old wives, stripeys and schools of small fish move through the reef, and rays rest on the sand. Coral bommies and seaweed beds add variety in the lagoon.

The drawback is exposure. Howies describes conditions as difficult on most days of the year, because swell over 1 m surges through the reef and wrecks visibility. The best days come after easterly weather in late summer and autumn, on glassy mornings before the sea breeze.

Mettams suits families, snorkellers and beginner divers on calm days, and experienced divers looking for an easy shore dive with good structure. It is busy on summer weekends, so go early. Water temperatures range from about 17 °C in winter to 22–23 °C in late summer. A sanctuary zone protects parts of the Marmion reefs, so look but do not take.

From the Mitchell Freeway take the Karrinyup Road exit and head west to the coast, then north along West Coast Drive; Mettams Pool is on the left past Trigg, about 15–20 minutes from the Perth CBD. There is ample street and roadside parking (it fills on summer weekends). The main entrance, just after Lynn Street, has steps down to the beach, toilets and a disabled-access ramp.

A second entry halfway down the hill uses a gravel and broken-concrete path and requires crossing shallow reef.

Perth's northern coast is far more exposed to ocean swell than the Cockburn Sound sites. Mettams is considerably affected by swell over 1 m, which surges through the outer reef and clouds the water, and it is poor on most days of the year. Dive when the swell is below 1 m and has been low for a couple of days, with light easterly winds.

The Fremantle Doctor sea breeze arrives around midday in summer and makes the lagoon choppy, so go early; glassy mornings are ideal.

Snorkellers stay in the sheltered lagoon. Divers enter from the main steps, cross the lagoon and head out through the reef to the outer edge in 4–7 m, exploring the swim-throughs, holes and arch, then return by the same gap. Avoid the 1.5 m inner pools for scuba.

Mostly dived and snorkelled independently; Perth dive shops run occasional guided shore dives and snorkel sessions in summer.