Water intended for human consumption should be "safe"and"wholeoome" i.e.free from pathogenic agent and harmful chemicals,pleasant to taste and usable for domestic purpose.In this study,an attempt has been made to work out for non point pollution of freshwater reservoir by nutrients (Nitrogen and phosphorus).Present study was carried out for a() fresh water lake in Ajmer,India.Ajmer is centrally located in the state of Rajasthan between 25°28′ North latitude and 73°58′ and 75°22′ East longitude.Total area of the Ajmer City is 241.56 sq.km.The city is situated in the mid of the desert zone on the one hand and humid zone on the other,thus having a zone of confluence.The climate is subtropical and is characterized broadly by three seasons viz.summer ( March to June),Monsoon (July to Sept.) and winter ( Nov.to Feb.).The temperature ranges from 14 to 40℃,the minimum being in winter and maximum in summer.Diurnal variations in the temperature were low during rainy seasons and mean temperature remains close to 25.1℃.Hot and desiccating winds of high velocity (30 to 36 km.per hour) are common.Agriculture and urban activities are major sources of phosphorus and nitrogen to aquatic ecosystems.Atmospheric deposition further contributes as a source of N.These non point inputs of nutrients are difficult to measure and regulate because they derive from activities dispersed over wide areas of land and are variable in time due to effects of weather.These nutrients support the fast growth of the aquatic plants ( mainly Azzola pinnata,Eichhornia crassipes,Hydrilla,Ceratophyllum etc.) as a result these factors lead to eutrophication,gradual shrinking of wetland area along with other complications like low light penetration,reduces oxygen concentration,clogging of water channels,lowers entertainment value of lake.The values of N and P in present study were found very high than standard liuits.Results show that this lake is highly polluted,eutrophic and highly productive.This high productivity leads to high bacterial populations and high respiration rates,leading to hypoxia or anoxia in poorly mixed bottom waters and at night in surface waters during calm,warm conditions.Low dissolved oxygen causes the loss of aquatic animals and release of many materials normally bound to bottom sediments including various forms of P and N.This release of P and N reinforces the eutrophication.Excessive concentrations of P is the most common cause of eutrophication in freshwater Lakes.