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Yudaganawa Lake was believed to be built by King Mahanaga in 3rd-century BC. The lake is spreaded across an area of 150 acres, and still provides water to 250 acres of paddy field cultivations. It was believed that the lake was expanded when it was dug further to supply clay to build the Yudaganawa Stupa.
King Mahanaga was believed to be the founder of Ruhunu Rata. He was a brother of King Devanampiya Tissa. His father King Mutasiva had 9 sons. After King Mutasiva’s death the eldest of his sons, Devanampiya Tissa became the king. According to the custom the rest of his brothers were in line to gain the throne before Devanampiya Tissa’s son. Ramadatta the consort of Devanampiya Tissa conspired to kill the Mahanaga thinking that her son could grain the throne sooner. One day when Mahanaga and some of his men were working in a field, Ramadatta sent them a basket of poisoned fruit, however her son ate those instead of Mahanaga. After this Mahanaga decided it won't be safe to live in Anuradhapura any more and fled to Ruhuna with his men and built the kingdom of Ruhuna.