Algae bloom in the Tai Lake is a major issue and affects the water supply to the surrounding cities greatly. Chlorophyll a (Chl-a) is a common indicator that represent the trophic status in lakes. Spatial and temporal variations of Chl-a concentration are analyzed on the basis of sample data at 21 sites during the period of 2001 to 2005. Data at the sites located in the Meiliang Bay, Zhushan and Wulihu show greater fluctuations than that at other sites. A general trend showing that high values in northern part and low values in southern part of the Tai Lake is observed in seasonal mean values of Chl-a concentration for four seasons. Most high Chl-a concentrations occurred in summer (June to August) and autumn (September to November). Quantitative relationships between Chl-a and other water quality factors are investigated at all sites. Relative good relationships are obtained between Chl-a concentration and other water quality factors during 2001 to 2004 by using partial least squared regression. Prediction of Chl-a concentration in 2005 with above models produce worse results, which may be due to the occurrence of some extreme high values of Chl-a concentration in that year. Even though, acceptable predictions are obtained at several sites. Since the water quality in the lake is affected greatly by the inflow of nutrients from rivers, these relationships will be helpful for monitoring Chl-a variation with the combination of hydrological models that is able to simulate the inflow of nutrients.