Sno – short for South North Opal – is one of the most versatile sites on Opal Reef. Scuba IQ calls it pretty much the perfect dive site with something for everyone, with sharks, turtles and lionfish, and Calypso uses it as its second dive of the day, running certified divers to the reef wall by tender. Wavelength snorkels it and describes a dramatic wall with boulder corals that has recovered from past crown-of-thorns starfish damage.

The wall drops from the reef top at about 5 m to sand at around 16–18 m. It is covered with boulder corals, sea fans and soft corals, and cut by ledges where lionfish hover and moray eels hide. Diveplanit's account of a Calypso dive here records a 16 m maximum and 48-minute dive with blue-lined rabbitfish, sea fans and several species of butterflyfish.

Turtles are regular, often resting against the wall or feeding on sponges, and reef sharks patrol the base. The reef top is the other asset. Shallow, colourful and sheltered, it gives snorkellers excellent viewing and lets divers finish with a long, relaxed safety stop among reef fish – the Calypso crew note that on these Opal sites you can do your safety stop on a 5 m part of the reef.

Sno's recovery from crown-of-thorns outbreaks is a good-news story; Wavelength's biologists point it out as an example of reef resilience, and coral cover has rebounded on the wall. The site suits all levels. New divers can stay shallow on the reef top and upper wall, while experienced divers can explore the base of the wall and look out for sharks.

Visibility is usually 15–30 m. Along with Bashful Bommie, Sno is one of the core sites of the Calypso Opal day.

Boats to Opal Reef leave Crystalbrook Superyacht Marina on Wharf Street, Port Douglas; Calypso Reef Cruises checks in around 8:15 am for a 9:00 am departure and returns about 4:30 pm, and Wavelength and Scuba IQ/Blue Dive leave around 8:00 am. Park in the marina car park or on surrounding streets (free all-day parking along Wharf/Dixie streets), or use the operators' courtesy pick-ups from Port Douglas and the northern beaches. Opal is about 60 km north-east of Port Douglas; the crossing takes 80–90 minutes, part of it threading through the protected Tongue Reef maze.

Divers gear up on board and enter by giant stride at a mooring; on Calypso some sites are reached by tender from the main vessel. The skipper chooses three sites on the day depending on wind and tide.

Opal is a crescent-shaped outer reef near the continental shelf edge. Its shape gives some shelter from the south-east trades that blow from about April to September, so several moorings (Bashful, Sno, Blue Buoy) stay diveable in 15–20 knots, but a 25-knot-plus trade wind makes the crossing rough and operators may cancel. Exposed sites on the seaward face and in the channels between North, Middle and South Opal are dived only in light winds and suitable tides.

October–December is typically calmest with the best visibility; the wet season (December–April) brings northerlies, storms, cyclone risk and marine stingers (November–May). Tidal currents run through the gaps between the Opal reef sections and around bommies, strongest on spring tides – channel and bommie sites are timed for neaps or slack water.

Descend to the base of the wall at 16–18 m, follow it with the wall on one shoulder, checking the sea fans and boulder corals, then come up to 5–8 m on the return and finish on the reef top, which is shallow enough for a relaxed safety stop.

Calypso Reef Cruises – daily Opal trips (3 dives/snorkel sites); Wavelength Reef Cruises – snorkel-only daily trips to exclusive Opal moorings; Scuba IQ / Blue Dive and Tech Dive Academy – small-group dive days several times a week; private charters.