ABSTRACT
Aquatic macroinvertebrate diversity in the Bhagirathi river was monitored for the period of twelve months (September 2004 to August 2005) for assessing the impact of Asia's highest dam, Tehri Dam. Comparative data on diversity of macroinvertebrates revealed that the number of taxa in the downstream stretch, especially close to the dam was significantly reduced. The velocity of water current, hydromedian depth, turbidity, dissolved oxygen and the bottom substrates of the river were found drastically influenced due to the construction activities of the dam. Macroinvertebrate diversity (Shannon-Wiener Index) was altered from 3.44 to 1.98. The members of ephemeroptera and trichoptera were drastically influenced in comparison to other macroinvertebrates.