Abstract: Disclosed herein is a method for predicting a chlorophyll-a concentration in a river using satellite image data and a nonlinear RANSAC method. In detail, the method includes (1) receiving a chlorophyll-a concentration, which was actually measured at a measurement station at a prescribed basin and an image from a satellite on a same date and at a same site as when and where the chlorophyll-a concentration was measured at the measurement station, (2) correcting a distortion of the image received from the satellite, (3) applying the chlorophyll-a concentration actually measured at the measurement station and data of the corrected satellite image to a nonlinear RANSAC method to extract a second-order function, and (4) inputting corrected data of a satellite image collected at the prescribed basin to the extracted second-order function to predict a chlorophyll-a concentration at the prescribed basin.