Greens Pool is one of the most famous swimming and snorkelling spots on the Western Australian south coast: a turquoise lagoon sheltered behind a row of rounded granite boulders in William Bay National Park, 15 km west of Denmark. Elephant Rocks, a short walk east, is a cove of huge granite boulders said to resemble a herd of elephants wading into the sea.

The snorkelling is shallow – 1-3 m in the main pool – over white sand, with submerged boulders forming channels and chasms that are fun to explore. The granite is covered in kelp, coralline algae and encrusting life, and fish are plentiful: tarwhine, wrasse, silver drummer, zebrafish, bullseyes, morwong, King George whiting and juvenile snapper, with sea hares and mosaic sea stars on the rocks and stingrays over the sand.

This is a snorkel site rather than a scuba destination. Scuba divers can dive the slightly deeper areas along the boulder line, but depth rarely exceeds 5 m and the site is crowded in summer. It is outstanding, however, for families, beginners and photographers, and on a calm morning the colours are spectacular.

Facilities include toilets, picnic tables and lookouts, but parking is limited and fills quickly in peak season. There is no camping in the park. The broader Denmark coast has dangerous beaches with rips and big swell; Greens Pool is the protected exception, though currents do occur at its western end in larger swell. Arrive early in the morning in summer for a parking space, calmer water and fewer people, and bring your own drinking water and shade – there is no shop at the park. Denmark town, 15 minutes away, has cafés, supermarkets and accommodation.

From Denmark drive west on the South Coast Highway for about 12 km and turn left at the William Bay National Park sign onto William Bay Road; follow it to the Greens Pool car park (about 15 km, 15-20 minutes). A short path with steps leads down to the beach. Elephant Rocks is a 10-minute walk east along a path from the same car park (or its own car park), with steps down into Elephant Cove.

The car parks fill early in summer and school holidays.

A line of granite boulders across the mouth of Greens Pool breaks the Southern Ocean swell, so the pool is usually calm even when the coast is rough. In large south-westerly swells water surges through the gaps and DBCA warns of strong currents, particularly toward the western end. Elephant Cove is more exposed.

Summer mornings are calmest; winter storms make both unsuitable.

Enter from the beach and snorkel along the inside of the granite boulder line, exploring the channels and chasms between rocks, staying away from the gaps at the western end where current funnels through.

No dive operator – independent snorkelling (hugely popular with tourists in summer). Nearest air fills in Albany.