Sia Lagoon is an offshore lagoon located along the North Coast of Egypt, near the city of Alexandria. The lagoon is part of an expansive region of lagoons and shallow coastal areas known as the Mediterranean Sea lagoons. It is one of the most important areas for migrating and wintering birds in Egypt.

The lagoon provides a habitat for many different species of fish, as well as birds, reptiles and mammals. It is also a key area for many species of endangered and threatened birds, including the glossy ibis, lappet-faced vulture, greater white-fronted goose, western reef heron and great white pelican.

The lagoon is home to two marine protected areas, or Marine Protected Zones (MPZs). These MPZs are managed by the Nature Conservation Sector under the Ministry of Environment and protect the marine life within the lagoon, as well as its biodiversity.

In addition to providing protection to wildlife, Sia Lagoon is an important source of food for nearby communities. For centuries, it has provided sustenance to villagers living in the surrounding areas, and its waters have been used for commercial fishing and aquaculture.