is an ancient reservoir in Anuradhapura, Sri Lanka. It was built by King Dhatusena around 400 AD. This reservoir has a circumference of 40 miles (64.4 km) and has a total area of seven square miles 7 square miles (18.1 km) at full capacity.
The pinnacle of irrigation work by King Dathusena was Kalawewa. The benevolent king considered the waters his wealth and treasure. There is rich folklore based on Kalawewa. All those are stories of human interest.
Historical sources indicate that King Mahinda the II (777-797) has expanded Kalawewa.
The modern history of Kalawewa begins with rehabilitation work commissioned by the governor, Sir William Gregory during the British Period. In 1958 the bund structure was rehabilitated to combine Kalawewa to Balaluwewa.
Irrigation uncertainties of Kala Oya valley came to an end once the Mahaweli waters reached Kalawewa in 1976.
Today Kalawewa is a key reservoir in the Mahaweli System. It endows Mahaweli H Zone with hydrological lifeline. Kalawewa also is a beauty spot within the Mahaweli System.
Specifics of Kalawewa
| Catchment | 598 Sq. Km. |
| Length of Dam | 6500 m. |
| Height of Dam | 14.08 m. |
| Capacity | 123.35 millions cu. m. |