[en] Observations and evaluations of thermal effects in the lake near the RAPS-1 REACTOR, are reported. The coolant waters are drawn from the lake at a depth of 8-10 m below the surface and discharged through an open channel with a temperature rise of 10deg C. Temperature profiles and spread in the velocity of the outfall are mapped using in situ monitors. These studies show evidence of thermal stratification in the period following winter and the existence of a well established thermocline. Parasitism and eutrophication are also observed. The thermal effects are found to be accentuated by photosynthetic effects. Proposal to utilise waste heat for algal culture in the Kalpakkam nuclear site in South and mariculture (lobsters, prawns) in the heated effluents canal at the Tarapur Atomic Power Station near Bombay are discussed. (K.B.)