Harsha Tharanga - Google
In 1981 during the excavations carried over to build a sluice at the south end of the Maduru Oya reservoir an ancient sluice was discovered which belonged to the Anuradhapura Era. Radiocarbon tests have revealed that this sluice was built in the 1st century BC, but archeologists and historians believe that it was built by King Kuta Kanna Tissa.
Records of Mahavamsa suggest that this was made in the times of Mahasen during the 3rd-century. The old bund was also buried and when found it measures at 219 feet long, 30 feet wide and 30 feet tall. It is a fine example of the hydrological engineering marvells of ancient Sri Lankan. The sluice was made with bricks and stone slabs.
As the name suggests the dam is built across the Maduru Oya and holds a water capacity of 596 million cubic meters. However access to the dam or the ancient sluice is restricted unless you present a permission letter from the Mahaweli Authority at the military checkpoint.