Spectral reflectance data, including irradiance reflectance (R_t) and remote sensing reflectance (R_rs, sr^-1), and colored dissolved organic matter (CDOM) absorption coefficients a_CDOM(440), were collected in the Saginaw River and Kawkawlin River plume regions of Lake Huron. We developed an empirical band ratio algorithm to derive a_CDOM(440) that could be directly applicable to Landsat-8 imagery. A model ranking method is used to determine the best band ratios as well as their empirical functions. One problem of previous CDOM estimations from Landsat imagery is that they usually use R_t or R_t/π rather than the real R_rs as the input data, but as a result of our study, algorithms derived using R_rs performed much better than using Rt. The green/red band ratio gave the best accuracies by fitting with power and exponential models (power model: R² = 0.819 and RMSE = 0.889 m^-1 and exponential model: R² = 0.829 and RMSE = 0.863 m^-1). The power and exponential models were further validated using an independent data group, achieving excellent results with the RMSE of 0.642 and 0.504 m^-1, respectively. The application of the exponential model a_CDOM(440) = 40.75e^-2.463x, x = R_rs(B3)/R_rs(B4) on two Landsat-8 images demonstrated that estimating CDOM from to Landsat-8 imagery has potential applications for monitoring water quality in long term and large scale.