The visible and near infrared bands of the Landsat thematic mapper (TM) were used in an empirical assessment of submerged vegetation biomass in Honghu Lake in the middle reaches of the Yangtse River, in the People's Republic of China. The method used here was based on eigenvector rotation of the four bands to enhance submerged vegetation biomass variations. Field measurement of spectral reflectance of submerged vegetation was taken for various biomass and vegetation types to determine the possibility of estimating submerged vegetation biomass using remote sensing. The locations of sample points were determined by global positioning system (GPS) and field biomass was obtained at the same time as the TM image. Regression analyses were performed between the principal components and biomass, and a marked linear relationship between submerged vegetation biomass and first two principal components (PC) was revealed. This was used to determine the total biomass of submerged vegetation.