The Tam Giang - Cau Hai lagoon system of Hue City stretches in the Northwest - Southeast direction along the coast, with a length of 68 km and a total surface area of 216 km². It comprises three interconnected lagoons: Tam Giang, Thuy Tu, and Cau Hai. With aquatic flora and fauna considered among the richest in Southeast Asia, this ecosystem has sustained generations of local residents.

Spanning a total water surface area of more than 210 km², Tam Giang - Cau Hai lagoon system,consisting of three main lagoons: Tam Giang, Thuy Tu, and Cau Hai, is often praised as a natural masterpiece bestowed upon Hue. The Tam Giang - Cau Hai lagoon system connects to the East Sea via the Thuan An inlet (Tam Giang lagoon) and the Tu Hien inlet (Cau Hai lagoon). It is the largest brackish lagoon system in Vietnam as well as all of Southeast Asia with an incredibly rich and diverse ecosystem.