THE CROSS ROADS: 20-22mts

The dive

The Cross Roads is a named section of the reef around Gurrig Island in the Magharee Islands, off Castlegregory in Co. Kerry, and it is dived from Scraggane Pier by Waterworld Dive Centre, which is the source of the name and of every published description of it. Waterworld's own list reads it as possibly the remains of an ancient river gorge crossing paths with another, and gives the working depth as 20 to 22 m. It is one of five dives the centre names on this island alone (with OverHang, Letter Box, the Inner Reef and the Outer Reef), all inside about 400 m of this pin, so this is a route on a reef rather than a separate piece of sea.

The reef around Gurrig is documented far better than the dive is, because BioMar dived and described three stations on it in May 1996. The station north-east of the island, about 600 m from this pin, found exactly the ground the operator's name suggests: a gully with a coarse sandy-gravelly bottom, surrounded by limestone bedrock thrown into ridges with intervening furrows, the furrows running down to about 21.6 m and the ridge tops at about 18.7 m. Red algae dominated the rock with patches of sponge and hydroids, the rock was heavily pitted and bored, and the surveyors noted a lack of brown algae and surprisingly few crustaceans or anemones. The station north-north-west of Gurrig, about 560 m away, found the same ridge structure deeper, at 22.9 to 27.9 m, with the large sea squirt Diazona violacea frequent on it. The station off the south-west side reported considerable surge.

NPWS designated the whole island group a Special Area of Conservation for reef: Carboniferous limestone, exposed on the west coasts and sheltered on the east, with moderately strong tidal streams running between the islands, and reef built from boulder, cobble, pebble and sand over areas of solid bedrock. It reads the foliose red algae and Sertularia argentea community at the 19-28 m band that this dive sits in as evidence of tide-swept ground, and records Diazona violacea and the sponge Thymosia guernei on the reef north-west of Gurrig. Both turn up in the occurrence records around this pin.

What Waterworld says you see is shoals of pollack and mackerel, with lobster, crawfish and crabs sitting in the crevices. Occurrence records within 1.5 km back the pollack, lobster, edible crab, spiny spider crab and velvet swimming crab, and add the animals a cold-water reef diver actually notices: elephant hide sponge and boring sponge on the rock, spiny starfish, edible sea urchin, cotton spinner, leopard-spotted goby, ballan wrasse, goldsinny and rock cook, long-spined sea scorpion and tompot blenny. Bottlenose dolphin and ocean sunfish are both on record nearby. Visibility across the centre's sites averages about 20 m, with 40 m on the best days and about 7 m on the worst.

• Crossed rock gorges at 20-22 m, the operator's reading of two meeting river channels
• Limestone bedrock in ridges and furrows, furrows to about 21.6 m and ridge tops at 18.7 m, per the 1996 BioMar station off the north-east of Gurrig
• Heavily pitted and bored rock under foliose red algae, with patches of sponge and hydroid
• Diazona violacea frequent on the deeper ridges north-north-west of the island
• Pollack and mackerel shoals, lobster and crawfish in the crevices, per the operator
• One of five named Waterworld dives on this island, all inside about 400 m

Conditions

Limestone reef between exposed Atlantic islands, boulder and cobble over bedrock, tide running through the channels. Waterworld publishes about 20 m visibility on an average day, 40 m on the best and about 7 m on the worst, across its sites generally rather than this one. Water temperature runs 8 C at the start of the season to 17-18 C in July, August and September. The islands are exposed on their west coasts and more sheltered on their east, so which side of the group is diveable is a wind question on the day.

On current: NPWS describes moderately strong tidal streams running between the Magharee Islands, and reads the red-algae and Sertularia argentea community at the 19-28 m band this dive sits in as evidence of tide-swept ground. Surge matters too: the BioMar station on the exposed south-west side of Gurrig recorded considerable surge in May 1996, and the west coasts of these islands are the exposed ones. No source publishes slack-water times or a current rating for the Cross Roads itself, so the timing is the operator's call; Waterworld runs its two boats out at set times each day rather than to a tidal window it publishes.

Best months: Jun, Jul, Aug, Sep