Hydrochemical studies were performed by collecting surface and bottom water sampled from 10 stations for a period of one year from February 1999 to January 2000 in a fresh water lake, Vellayani lake, in Thiruvanathapuram district, the capital city of Kerala. Marked spatial and temporal variations were noticed in majority of abiotic parameters. Temperature, turbidity, pH, conductivity, dissolved oxygen, biochemical oxygen demand, total solids, total suspended solids, total dissolved solids, alkalinity, chloride, hardness, nitrate, phosphate and silicate were found higher during premonsoon.