Nawarathna, T.N.T.K.Makehelwala, M.2022-02-082022-02-0820159789550481088http://www.erepo.lib.uwu.ac.lk/bitstream/handle/123456789/8303/20-MRT-Water%20pollution%20study%20in%20Nalanada%20Lake%20to%20improve%20the%20Water%20.pdf?sequence=1&isAllowed=yWater is the largest natural resources of Sri Lanka although only a relatively low percentage of total population is getting safe and clean water for daily use. Water is using for Drinking, bathing, washing, and cleaning. Beside it is used for agriculture, industrial, hydropower generation. The Nalanda reservoir located in Naula, Matale district is the main water source of Naula Water Treatment Plant of National Water supply and Drainage Board (NWSDB). On the other hand NWSDB faces a big problem in the dry season because pumping water had a less amount of Dissolved Oxygen (DO) and occurring black color in pumping water. The dissolved oxygen (DO) concentration is a primary measurement of a stream’s healthiness. The dissolved oxygen concentration responds to the biochemical oxygen demand (BOD) load. Investigators have continuously studied the dissolved oxygen uptake characteristics in stream water in relation to different sinks and sources in order to develop mathematical models describing the DO consumption. In this reservoir percent high amount of Algae due to high nutrients content such as nitrate and phosphorous and change that algae type seasonally. One of the objectives of this research study is that Nitrate and Phosphorus variation in reservoir. And Main Objective was identification of the Dissolved Oxygen (DO) Variation in Nalanda reservoir. Methodology In this study six sampling location points were selected and studied the variation of nitrate, phosphorous and DO of these sampling points for four weeks of time. These data were collected in rainy and dry season. Samples were collected from the different distances from the intake of Naula Water Supply System. Totally 24 samples were collected from the upstream of the reservoir. Basically, the selected pollution points are surrounding point of the reservoir. Samples were taken from different morphological units of the reservoir. DO was analyzed at the sample collected points and COD and BOD also analyzed using the Standard laboratory procedures. Finally DO concentration variation was analyzed by using mathematical model called Streeter- phelps. Results and discussion Eutrophication of water body is occurred under high nutrients. The nutrients such as nitrate and phosphate distribution within selected pollution points in Nalanda reservoir is shown in figure 1. The recommended phosphate level for maintaining healthy water to minimize algae growth is 0.1 mg/L and nitrate level is 10 mg/L (USEPA). The results shown below indicated that the nitrate level was within required limit and phosphate level was exceeded limit. Therefore, phosphate consuming algae species can occur in Nalanda reservoir during this period.enMineral SciencesMaterials SciencesScience and TechnologyWaste Water TreatmentWater PollutionWater qualityOther