Cardiff Bay, one of the largest man-made freshwater lakes in Europe, was formed in April 2001 when two of the main rivers in South Wales, United Kingdom were impounded by the construction of a barrage. The water quality of Cardiff Bay has been intensively monitored, primarily due to the wetland reserve which was undergoing a fairly steady succession from the previous estuarine habitat. The present study was carried out to investigate the physical, chemical and biological quality of water in Cardiff Bay. Seven water quality parameters namely pH, biochemical oxygen demand (BOD), Ca, Mg, Cl, total hardness and total suspended solids (TSS) were analyzed for a period of five years from 2001 to 2005 to investigate their temporal variation in this study. The findings indicated that variations in water quality across Cardiff Bay were small during this period. In general, pH, BOD, Ca and hardness showed a slightly increasing trend as opposed to Cl which decreased. Mg was temporally homogeneous and TSS varied inconsistently. A comparative study was conducted against the relevant data obtained from Sasthamcotta Lake in Kerala, India in which higher values of pH, Ca and Mg were observed in Cardiff Bay. The necessity for long-term data sets was highlighted due to the observed lack of correlation among the indicators, which therefore suggests that a long-term monitoring is imperative in assessing the water quality trend as well as management strategies.