Nutrient entrance into lakes and eutrophication is a serious problem in the world which intensifies the growth of algae. Remote sensing technology could provide overall area information on chlorophyll-a. In this research Landsat 8 imagery was used to extract an empirical model for estimating the concentration of chlorophyll-a and TSI (Trophic State Index). Some 76 samples were collected in this study. 30 samples were collected in July, 2014, 20 samples were collected in January, 2015 and 26 samples were collected in May, 2016. The value of DNs were converted to reflectance. Several conversions such as band ratio, power, square root, exponential, log and NDI (i.e. Normalized Difference Index) of reflectance values were used to select the most accurate regression model of chlorophyll-a concentration and TSI. Results of the study showed that the best model for chlorophyll-a concentration and TSI was based on band ratio and NDI of bands reflectance. The values of adjusted R2, SE and NRMSE were 0.81, 0.26 and 0.11 respectively for chlorophyll-a model based on band ratio. Also the values of adjusted R2, SE and NRMSE were 0.79, 0.04 and 0.1 respectively for TSI model.
