The extensive Snake River floodplain in Northwest United States has experienced major changes in water channels and vegetation types due to floodings. To detect the change of wetland cover-types for the period of 1985 and 1988, post-classification comparison and image differencing change detection techniques were evaluated using Landsat-5 TM digital data. Differenced infrared-band images indicated better accuracy indices than any visible-band images. A thresholding technique was applied to identify the change ;ind no change categories from the transformed images produced by image differencing, The problems in using different accuracy indices, including the Kappa coefficient of agreement, overall accuracy, producer`s accuracy, user`s accuracy, and average accuracy(based on both the producer`s and user`s accuracy approaches) in determining an optimal threshold level, were examined.