Cau Hai Lagoon is a break in the Tam Giang - Cau Hai. Area of the Tam Giang lagoon about 52 km², stretching about 24 km to the west northwest - east southeast from the mouth of Lau River to the mouth of the river, in the territory of three districts is Phong Dien, Quang Dien, Huong Tra, Thua Thien – Hue province. Tam Giang Lagoon about 11% of the coastal lagoon area of Vietnam. This cutting depth of 2-4 m, where up to 7 meters deep. Every year on the lagoon exploitation thousands of tons of seafood, fish, shrimp all kinds. Currently there are plans to build research investment over Tam Giang Lagoon Bridge to conditions of economic development and tourism in the region.
