Parakrama Samudra, the Sea of King Parakrama as the name literally means, is a shallow reservoir with a surface area of 22.6 km2. It consists of three separate reservoirs connected only by narrow channels at low water. The northernmost reservoir is the oldest and referred to as Topa wewa (Sinhalese wewa=lake or reservoir). The middle section is Eramudu wewa and the southernmost portion at the highest elevation is Dumbutula wewa. Topa wewa was built around A.D. 386. The other sections were added and the reservoir expanded during the reign of King Parakrama Bahu the Great (A.D. 1153-1183).

Lake Parakrama forms one of the larger reservoirs of an ancient, intricate and sophisticated water storage system for the irrigation of rice fields in Sri Lanka. During the twelfth century A. D. it was situated in the capital of Sri Lanka and in a densely populated area, judging from the extensive ruins of a magnificent civilization. Later the area was abandoned, the city reverted to jungle, and the lake was drained due to damage to the dam. The reservoir was restored to its present status about thirty years ago, and the surrounding area has attracted increasing numbers of immigrants, mainly rice cultivators and more recently fishermen.

Lake Parakrama has a catchment of about 75 km2. This consists mainly of a forest reserve which is limited by high ground in the west. The reservoir is supplied by water from rainfall in its catchment carried by small streams and also by a channel running north from a small river. Water from the river traverses a distance of about 8 km before reaching the lake. Considerable amounts of silt are deposited in the channel and do not reach the reservoir. The stored water is supplied mainly for the irrigation of rice fields. There has been encroachment on the forest reserve by fishermen in the last twenty years.

Human use of water for domestic purposes has grown with settlement of a large number of immigrants in the vicinity of the lake. The lake receives a considerable load of faecal pollution from the human population in the vicinity. During the low water season when large areas of the lake bed are exposed, cattle graze on the lush growth of grass and leave considerable quantities of faeces behind, enriching the lake (1).