A 35.0 mile segment of the North Anna River, Virginia is currently being impounded to provide cooling water for a nuclear reactor. The headwaters of a major tributary of the North Anna River, Contrary Creek, was the site of extensive pyrite mining operations at the turn of the century. Contrary Creek is a source of acid mine drainage, and confluences with the North Anna River approximately midway through the pre‐impoundment basin. The sequential comparison method of establishing diversity indices of community structure was used to evaluate the effect of acid mine drainage on the macrobenthos in a 21.5 mile segment of the river. The diversity indices indicated that the North Anna River recovers from acid mine drainage approximately 19.0 miles below the entrance of Contrary Creek or 2.0 miles below the present dam site. However, the molluscan element, which occupied 32% of the macrobenthos at the upstream control station, did not show a reoccurrence within the study area below the discharge of Contrary Creek. The lack of mussel recolonization indicates that the river has only partially recovered from the acid drainage. Even though the Sequential Comparison Technique provides a rapid method of gathering numerical information regarding biological water quality, the technique as currently used does not exhibit sufficient resolution to distinguish between different degrees of biological recovery.