Aquatic insects are used as model organisms for assessing the health status of lenthic or lotic ecosystems. Biomonitoring using entomological indicators is one of the widely accepted tools to analyze the impacts of sewages in aquatic environment. The present study was aimed to assess the health status of a semi urban river system, Killiyar using entomological indicators. Season wise sampling of aquatic insects was done at four selected segments according to the rapid bioassessment protocol recommended by Environmental Protection Agency. The present study could identify 29 families of aquatic insects for screening the levels of pollution in Killiyar. Family Biotic Index (FBI) showed that there was a remarkable variation in water quality along the river. Hilsenhoff’s family biotic index obtained for river origin was in the range 4.40 - 5.02 indicating excellent water quality. High value of family biotic index, least occurrence of intolerant groups and dominance of tolerant taxa in the midstream and downstream segments showed that increased contamination of water by various sources. Immediate attention is needed to cease the degradation of this precious ecosystem.      Keywords: Aquatic insects, Biomonitoring, Family Biotic Index, Killiyar, Water pollution