The western lagoon of the southern atoll laps along the whole eastern shore of West Island, and with the settlement, airport and accommodation all on this island, it is the most accessible water on Cocos. It is not a single named site but a stretch of shallow lagoon: sand flats and seagrass with scattered coral patches, clear and warm, where juvenile blacktip reef sharks patrol the shallows, green turtles feed on the seagrass, rays rest on the sand and small reef fish gather around the coral. The official tourism material and travel features describe the lagoon's turtles and juvenile sharks as a highlight for visitors, and the marine park management identifies the lagoon's seagrass and green turtle habitat as key values.

For structured snorkelling, Pulu Maraya off Scout Park and Trannies Beach at the northern end are the named West Island spots; elsewhere along the shore, visitors can simply walk in and explore. The lagoon is also Cocos' kite-surfing arena in the trade-wind season, which makes some beaches busy with kites on windy afternoons. Because the water is very shallow over large areas, snorkelling is best at mid to high tide.

It suits families and anyone wanting a quick swim close to accommodation. Many visitors on Cocos for a week or more use the lagoon daily – a morning snorkel before the wind rises, a paddle on a kayak or SUP to look over the seagrass for turtles – and it is the backdrop to life on West Island. Juvenile blacktips are harmless to people and quickly move away.

From the West Island settlement, walk, cycle or drive to any of the lagoon-side beaches along the island's eastern shore; access tracks lead off the main road to the water. Park at the track end and walk to the beach. Snorkel gear can be hired at the visitor centre.

The lagoon is shallow for a long way offshore, so snorkelling is done over flats and scattered coral close to shore; pick a spot with some depth at mid to high tide.

Lagoon snorkelling is possible year-round, but the south-east trades (April/May–October, often 15–25 knots) chop the lagoon, stir up sand and make swimming harder; the doldrum season (November–April) usually brings glassy conditions and the clearest water. Tides matter more than swell inside the lagoon: shallow flats can become too shallow at low water, and tidal streams run through channels between islands. Heavy tropical showers are brief and have little effect on visibility because there is no river run-off.

The West Island lagoon shore is sheltered from ocean swell but fully exposed to the south-east trades, which blow across the lagoon onto this shore; calm mornings and the doldrum season are best. At low tide much of it becomes too shallow to snorkel.

Choose a beach at mid to high tide, enter from the sand and snorkel over the seagrass and coral patches parallel to shore. Watch for juvenile blacktips and turtles, and keep clear of any kite-surfing areas.

Self-guided; no operator required. Kayak and SUP hire is available on West Island for exploring the lagoon.