Human activities have affected the biodiversity of Lake Tana. Hence, this research evaluated water quality of Lake Tana by measuring biotic indices. Biotic diversity (Shannon-Weiner diversity index, H) was 3.07 in the dry season and 2.50 in the wet season. The impacted sites’ biotic diversity was H’ = 2.94 in the dry season and 2.49 in the wet season. Hence, diversity was more in the dry season. Thus, Lake Tana water quality is poorer in the wet season than the dry season. Simpson’s diversity index (“D”) of Lake Tana in the wet season was 0.87 and in the dry season 0.94; for impacted sites D = 0.89 in the wet season. In general, the highest “D” value, observed in the dry season, indicates highest organism diversit;, which indicates better water qulity in the dry season than the wet season. Txa Richness (TR) scores indicated poor water quality. EPT index of Lake Tana was 13.2 %; evidence of water quality degradation. Generally, Lake Tana Biotic Indices showed that the ecological potential of Lake Tana is in the range from “Good” to “Bad or very poor”, where the water quality is unfit for domestic purposes.
Keywords: Biotic scores; Shannon-Weiner diversity index; Simpson’s diversity index; txa richness; ecological potential