Chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), and dissolved organic carbon (DOC) are important indicators tracing lake water quality, but their measurement processes are time-consuming and require a large amount of reagent, manpower and material resources, and discharges harmful waste during measurements. Chromophoric dissolved organic matter (CDOM) is the fraction of dissolved organic matter (DOM) that can strongly absorb light at the ultraviolet region. The CDOM measurement is time-saving and convenient, and environmentally friendly, and the optical indices of CDOM can be used to trace lake water quality. We collected samples from 32 sampling sites in Lake Taihu for three occasions in February, May and August of 2016, using spectral absorption and the combination of excitation-emission matrices and parallel factor analysis (EEMs-PARAFAC) to explore the optical variability of CDOM in Lake Taihu and the applicability of using CDOM indices to trace the variability of BOD₅, COD, and DOC concentrations. Three fluorescent components were identified using EEMs-PARAFAC, including a humic-like C1, a tyrosine-like C2, and a tryptophan-like C3. COD, BOD₅, DOC and the optical indices of CDOM all showed similar spatial distribution trends with the highest values of these indices in different hydrological scenarios being found in Zhushan Bay and Meiliang Bay in the inflowing regions of the lake. The means of COD, BOD₅, DOC, and humic-like C1 in the rainy season were all significantly higher than those in the dry season and the wet-to-dry transition season. We found no significant difference between the mean of a₂₅₄ during the rainy, dry season, and the wet-to-dry transition season. The means of protein-like C2 and C3 were significantly higher in the dry season and wet-to-dry transition season than those in the rainy season. In different hydrological scenarios, COD, BOD₅, and DOC are all significantly positively correlated with a₂₅₄ and humic-like C1, and the linear correlation between COD, BOD₅, DOC and CDOM indices in Lake Taihu in the rainy season is better than that in the dry season and wet-to-dry transition season. CDOM optical indices including a₂₅₄, C1, C2, C3 are potential indices tracing the variability of COD, BOD₅ and DOC and are useful indicators tracing water quality in Lake Taihu and potentially a wider aquatic environment in different hydrological scenarios.