Batticaloa, better known simply as Batti, is the regional centre of Sri Lanka's southeast coastal area. The Portuguese were the first to erect a fort here in 1572. The Dutch claimed it in 1638, handed it over to the Kandyans in 1643, but reoccupied and modified it in 1665. In 1795 it was surrendered to the British, and it still stands today by the banks of the Batticaloa Lagoon. Although the interior is now an administrative office, the exterior is still in good condition with unbroken square walls, a bastion in each corner, and a moat that still holds water. 

However, Batticaloa's most celebrated attraction is not its fort but its singing fish. Between April and September, in particular on moonlit nights, strange sounds emanate from the waters of the lagoon. They have been described by some as being like the tuning up of a string orchestra, while others say they are more akin to musical chords or the vibrations of a wine-glass, when its rim is rubbed by a wet finger. To experience these sounds clearly it is best to take a boat into the middle of the lagoon, thrust a pole into the shallow, muddy bottom, and hold it to one's ear. The source of these sounds has been the subject of much controversy. Some believe that they are caused by species of mollusc living in the lagoon, while others maintain that topsail catfish, which congregate in great numbers in the lagoon during the April-September period, are the cause. Still others suggest that the sounds are created by tidal water flowing through holes in rocks at the bottom of the lagoon.