Under the Mexican Constitution beaches are Federal property.

To be denied access to a beach - property of the Federal Government of Mexico - is a violation of a Revolution ideal as expressed in the Constitution.

¡Viva la Revolución, pero aún no ha terminado!

this question has come up recently in Yucatan adn Quintana Roo.
Is there such a thing in Zihua?

The local government is accused of allowing the privatization of beaches. The Blue Flag rule alone makes many locals and visitors simply feel unwelcome at those designated beaches. Playa Contramar in Zihuatanejo Bay has had most of its beachfront privatized and altered by "influential" people. Playa Las Cuatas, Playa Don Rodrigo, Playa Hermosa, and Playa Don Juan in Ixtapa have all been essentially privatized. The local government has knowingly turned a blind eye to all this.