Songkhla Lake is the largest natural lake in Thailand. It is on the Malay peninsula in the southern part of the country. Covering an area of 1,040 km2 it borders the provinces of Songkhla and Phatthalung. Despite being called a lake, this water feature is actually a lagoon complex geologically.
The lake is divided into three distinct parts. The southern part opens with a 380 m wide strait to the Gulf of Thailand at the city of Songkhla. Here it contains brackish water about half the salinity of seawater. Further north, after a narrowing to 6 km width, is the Thale Luang (782.80 km2). At the northern end between mangrove swamps is the 28 km2 Thale Noi in Phatthalung Province. The most striking feature is the long 75 km long spit which separates the lake from the sea. Unlike most spits, it was probably formed when originally existing islands were connected by silting from the lake precursor.
The Phru Khuan Khi Sian wetlands near the Thale Noi Lake have been protected as a Ramsar wetland since 1998. It is part of the larger Thale Noi Non-Hunting Area, created in 1975. A small population of Irrawaddy dolphins is found in Thale Luang, near the Si-Ha Islands of Phatthalung. They are threatened with extinction by overfishing and pollution.