Marine protected area of Capo Caccia - Isola Piana, Marine reserve in northwestern Sardinia, Italy.

Marine protected area of Capo Caccia - Isola Piana is a coastal reserve spanning over 26 square kilometers along northwestern Sardinia, defined by steep limestone cliffs that rise from the shore. The island of Isola Piana sits at its center, surrounded by clear waters and dotted with submerged caves that open into the rock face below the surface.

The site received official protection status in 2002 under Italy's environmental authorities to safeguard its marine habitats and archaeological resources. Thousands of years before this designation, early people inhabited this coastline and left traces in the caves, which today serve as windows into prehistoric human activity.

The area is home to underwater caves that have drawn people for thousands of years, and their ancient graffiti and artifacts tell stories of early visitors. Local communities today maintain a strong connection to these waters through traditional fishing practices and a deep respect for the marine environment.

The reserve is split into three zones: zone A is off-limits except for scientific study, while diving and professional fishing are allowed only in zones B and C. Spearfishing is banned everywhere. Cave diving and recreational rod or line fishing need a special authorisation. The Grotta di Nettuno can be reached on foot via the Escala del Cabirol or by boat from Alghero's harbour.

The red coral (Corallium rubrum) found in these waters has long been harvested for Alghero's economy and appears on the city's coat of arms. Near the Grotta Verde lies the reserve's only colony of cushion coral (Cladocora caespitosa), a single madreporarian formation that divers can look for.