The most noticeable feature in Tissamaharama is the giant man made lake, a tank, called Tissa Wewa. The Tissa Wewa is one of the four large ancient irrigation tanks in the area and is believed to be constructed the 3rd Century BC by King Yatala Tissa, or regional king Maha Naga who is a brother of king Devanampiyatissa (250-210 BC). Tissa Wewa is also an engineering marvel of the Sri Lanka’s ancient tank building technology, for the dam built across Kirindi Oya to divert water to Tissa Wewa is the first known oblique dam in the world which proves the level of knowledge the Sri Lankan Engineers had on handling large bodies of water. The Europeans understood the principles and concepts of the oblique dams only in the 18th Centaury – 2100 years later.
Today, water from the Tissa Wewa and the other tanks is used to irrigate the paddy fields near Tissa keeping the surroundings lush and green year round. Especially at dawn and sunset, the Tissa Wewa, part of the Wirawila Bird Sanctuary is a great place to see a variety of water-bird life.