Umm Usk

The dive

Umm Usk, written Sha'ab Umm Usk on most charts and given as Onghosh by local crews in the PADI record, is a horseshoe-shaped reef in the southern Strait of Gubal, between Gubal and Shadwan islands. The open ends of the horseshoe point south and enclose a lagoon. Seawolf Diving Safari says isolated coral formations at the southern tip cut the wave action, so the lagoon stays sheltered in almost any weather, and that shelter, not the diving, is why the reef appears on itineraries at all: boats tie up here for the night.

The dive is shallow and easy and the sources cannot agree on its numbers. The Wannadive atlas records 18 m average and 40 m maximum, visibility of 10 to 30 m, current under a knot, and dives made mainly on the west side with occasional ones north and southwest. A liveaboard listing quotes 9 m as the site depth against the same 40 m maximum. Seawolf, which is the only source that describes an actual route, drops divers by dinghy at the southeast and works anticlockwise round the reef ring, with the first ledge on the east side at about 20 m. We record 20 m as the working depth; the 40 m figure is the sand outside the reef, not the dive.

What is there is a reef ring rather than a single feature: Acropora structures, large coral heads, steep reef wall and mushroom-shaped pinnacles. Seawolf says the current mainly comes from the south and that you therefore have to keep close to the reef wall, which matters more than the sub-one-knot figure suggests, because the arms of the horseshoe open the same way the water is running.

The lagoon carries a resident group of bottlenose dolphins. Seawolf is careful about it: they can be watched going through their manoeuvres if they are not disturbed, and they leave if they are. Our own occurrence records for this pin are the thinnest of any Gubal site we hold, ten taxa in a 2.34 km radius, and the Indo-Pacific bottlenose dolphin is the only one recorded more than once. The rest is a night-dive list, sea goldie, Guenther's sweeper, yellowbar angelfish, pharaoh moray, a scaly clam and a Spanish dancer. One correction while you are here: our catalogue files this pin under Abu Nuhas, which is wrong. Sha'ab Abu Nuhas and its wrecks lie 5.4 to 6.5 km east-southeast, and nothing we read puts a wreck on Umm Usk.

• A horseshoe reef with the open ends pointing south, enclosing a sheltered lagoon
• Overnight mooring inside the lagoon, which makes this a standard night dive on Gubal itineraries
• Resident bottlenose dolphins in the lagoon, backed by the only repeated occurrence records at this pin
• Acropora structures, large coral heads and mushroom-shaped pinnacles on the reef ring
• Shallow enough that PADI's record lists it for confined-water training as well as diving

Conditions

A sheltered reef ring dived from a dinghy or off the back of a boat already moored inside it. A liveaboard listing gives water of 22 to 28 C across the year; Seawolf recorded 29 C on a summer safari and recommends a shorty. Because the lagoon is described as protected in all weather, this is one of the stops the strait keeps when wind closes the exposed ones.

On current: The sources agree the site is easy and disagree on everything measurable. Wannadive's atlas records current under one knot and a liveaboard listing says the site is unlikely to be affected by current at all, while Seawolf, the only source describing a route, says the current mainly comes from the south and that you have to keep close to the reef wall. Take the Seawolf version as the plan: light water most days, with a southerly set that will push you off the wall on the open faces, which are the faces the horseshoe opens onto. Depth is the bigger spread: 9 m as the site depth in one listing, 18 m average and 40 m maximum in the atlas, about 20 m at the first ledge on the east side per Seawolf. We record 20 m, the conservative working figure. Published visibility runs 10 to 30 m, too wide a band to reduce to a single number, so we record none. Position varies too: our pin comes from PADI and sits 2.4 km north of the coordinates the atlas gives for the same reef, so navigate off the boat's plot rather than either figure.