The Lagunienu is a small coastal stream in the southeast of the department of Corse-du-Sud, Corsica, France.

The Lagunienu is 7.27 kilometres (4.52 mi) long. It flows through the commune of Porto-Vecchio. There are no named tributaries. The stream rises to the northwest of the hamlet of Renajolo and flows in a generally southeast direction past the village of Palavesa to enter the Golfe de Porto-Vecchio between Poretta and Marina di Fiori. There are east-facing beaches on either side of the mouth of the Lagunienu.