Barra de l'Arbre

Mataro's most celebrated rocky ridge sits just minutes from port — a formation running parallel to the coast at 16-22 metres, with Posidonia meadows pressing against both flanks. Arrive at the rock-grass boundary and work along it slowly. This transition zone is where nudibranch numbers peak: the porous rock provides grip and shelter while the seagrass delivers nutrients. Move inward along the ridge's creviced spine to find lobsters wedged into hollows, morays peering from holes, and conger eels retreating deeper as your light finds them. Octopus roam the edges between dives, and damselfish schools hover above the Posidonia canopy on both sides.

What looks like a standard rocky ridge dive reveals itself as a Posidonia-edge habitat dive. While every Maresme ridge offers rock crevices and the usual Mediterranean cast, this one adds seagrass borders that no site in the Port Balis sector can match. That boundary — where hard substrate meets soft meadow — concentrates opistobranch species into a habitat corridor that pure rock formations cannot support. A local diving magazine placed it among the three most important Mataro ridges alongside El Negre and La Trencada — a well-dived site with over 200 recorded species that confirms sustained interest. The site's personality is macro photography: the nudibranch and invertebrate subjects cooperate.

Cameras are not optional here. Multiple sources specifically highlight nudibranch photography as the main draw — bring a macro setup if you have one, and a torch to illuminate the crevices where subjects shelter against the rock. The Posidonia borders are EU-protected, so boats anchor on sand rather than grass; your centre will brief you on entry points. Three operators run trips from Port Mataro — Blaumar, Mediterranean Dive, and Niman Sub — and the short boat ride means the ridge is commonly paired with El Negre or La Trencada for a two-dive morning. Depth sits comfortably within OW limits throughout the entire profile.