Abstract: Throughout the last century, riverine ecosystems have suffered from intense human intervention resulting in habitat loss and degradation and as a consequence, many fish species have become highly endangered, particularly in rivers where heavy demand is placed on fresh waters. River Achenkovil originating from the mighty Western Ghat mountain ranges reflecting the rich cultural heritage of Central Travancore is under the crushing pressure of environmental degradation caused by unprecedented human exploitation. A study has been conducted from February 2004 to January 2005 to document the fish diversity in the river system. A total of 52 species belonging to 5 orders and 18 families were collected. Cyprinidae was the most dominant family (68.50%) followed by Cichlidae (7.56%) and Ambassidae (6.73%). Results suggested that environmentalists and governmental agencies should pay responsiveness to protect the existing faunal wealth.