The water quality of many streams in Lake Victoria Basin, Kenya is affected by agricultural intensification, municipal and industrial effluent, as well as water abstraction, livestock and deforestation. Management efforts have been hampered by lack of clear standards against which to judge the degree of environmental degradation. To achieve this goal, a macroinvertebrate-based Index of Biotic Integrity was developed to monitor ecological integrity of selected rivers occurring in the same ecological zone in the upper reaches of the basin. Macroinvertebrates were sampled with a Surber sampler at 22 stations. The stations were grouped into three condition categories (reference, intermediate and impaired stations) according to the level of degradation. Twenty metrics representing the structural and functional organization of macroinvertebrates were computed using Mann-Whitney U tests. The separation power of the metrics was evaluated using box plots. Final metrics were evaluated for responsiveness by Pearson’s correlations with physicochemical parameters. Of the 20 metrics, 9 met the test criteria, as they displayed variability across the stations, and were used to provide the final scores for Macroinvertebrate Index of Biotic Integrity (M-IBI). Metric values at both reference and impaired sites were used to establish the scoring criteria using inter-quartile ranges. This index provided preliminary evidence of response to changes in ecosystem integrity exhibited by resident macroinvertebtrate assemblages in rivers in the upper reaches of Lake Victoria Basin. It was recommended that the index developed be used to assess and monitor rivers in the upper catchments of Lake Victoria Basin in Kenya.

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