
Posidonia Dive
SSI Diamond Instructor Training Center at Port Balis marina, 35 km north of Barcelona, running 24 boat dive sites on the Maresme coast year-round.
Deep Port Balis rocky ridge at 25-29m off the Maresme coast, with dense yellow tree-sponge clusters and a longer boat transit than its neighbours.
Last updated April 2026
The transit east from Port Balis runs about fifteen minutes — further than the centre's usual ten-minute hops to the closer ridges, and a small reset for divers used to a quick boat ride. The ridge sits at 25-29m, and the boat anchors directly on it without a fixed mooring buoy. Down the line, the structure runs roughly parallel to the coast, with a deeper, rockier west flank and a softer east edge that fades into sand. Most groups follow one side first and return shallower along the other, working back to the anchor along a guideline the centre lays across the rock at the start.
The west flank is where the dive earns its name in the local rotation. Dense clusters of yellow tree-sponge (Axinella verrucosa) cover stretches of rock. Tens of individuals, some unusually large, in numbers that mark this site out from the neighbouring ridges. A green-leafed algae stand grows alongside the sponges, dense enough to be worth flagging though the species is not yet positively identified. East of the highest section, the rock breaks down into mixed rock-and-sand transition where Flabellina nudibranchs sit on round sponges and the occasional dusky grouper holds station off the structure.
Macro is the working mode. Torches reveal Mediterranean moray and conger in the cracks. One unusually large red scorpionfish was observed in the open on a recent owner dive, a memorable encounter rather than a regular feature. Bottom time is tight on air at this depth, which is why Nitrox 32 is the local default for full coverage.
The yellow-sponge facies is the strongest single visual signature of El Pico. Axinella verrucosa is common across the Maresme, but the density seen on the west flank here lifts it from background decoration to a genuine framing feature for the dive. Combined with the green-algae stand, the result is a small ecological pocket that doesn't quite match what local divers find on the closer Port Balis ridges. The morphology, deeper west and softer east, also tracks closely with La Virgen, which makes the two natural macros-and-crevices companions on a two-dive day rather than redundant choices.
This is a Nitrox-friendly site, not a Nitrox-optional one. At 25-29m on air, no-stop bottom time is short and the dive ends before the divers are warmed up. EAN32 is widely available locally and meaningfully extends what a diver can see. A torch belongs in the kit because most of what makes this site distinct sits inside cracks. Compass and SMB stay standard practice on every dive at this depth. A centre line across the ridge eases return navigation but should not replace independent skills.
The 15-minute transit is long enough that Garbi (SW) days can make the boat ride uncomfortable; a calmer forecast is worth waiting for if the surface is up. Calibrate the suit to the bottom band, not the surface — the summer thermocline drops bottom temperature 3-4C below the surface reading at 25m. A 5mm with hood is the safer choice through the warm months; from November through April a drysuit or 7mm semi-dry is the right call. When diving with mixed gas in the group (some divers on air, some on Nitrox), confirm everyone's mix and NDL profile before descent. At this depth the no-stop windows for air and Nitrox 32 diverge enough to matter.
What makes this dive site stand out.
Dense Axinella verrucosa aggregations on the west flank stand out against neighbouring barras
25-29m bottom puts this in the Nitrox-helpful band, beyond the OW depth limit
About 15 minutes east from Port Balis, further out than most of the centre's rotation
Flabellina nudis, scorpionfish, moray and conger work best with a torch and time
41.5453°N, 2.5561°E
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SSI Diamond Instructor Training Center at Port Balis marina, 35 km north of Barcelona, running 24 boat dive sites on the Maresme coast year-round.

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Depth is the main demand. No significant currents reported. Navigation is straightforward along the ridge with the centre's anchor line for return.
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