Quantification of Environmental Water Requirement based on random percentage ofrnannual mean flow do not address the actual needs of the water dependent ecosystems, itrnpossibly overestimates or underestimate the requirements. Scientific communitiesrnworldwide are working to design an appropriate approach for the quantification of thernenvironmental water requirements for an interest area. Among their efforts," habitatrnbased approach" is a popular method in estimating environmental water needs. Thernenvironmental water requirement of Lake Abjiata is computed based on this approach byrnestimating the water requirement of Lesser Flamingos, which are dominant birds thatrnfeed on the lake but significantly reducing in number. Their water requirement wasrncomputed indirectly based on their food and energy requirement and on the waterrnrequirements of their main food, the microalgae known as Arthrospira Spirullina. Inrnaddition the estimation considers the direct evaporation from the lake and drinking waterrnrequirement of the birds, Therefore, this study estimated the environmental waterrnrequirement of Lake Abijata to support 108,275 Lesser Flamingos within 132 kmrn lakernarea as 221.8MCM. In addition the study evaluates the water balance of the lake tornsupport, this environmental water requirement and confirmed that the environmentalrnwater requirement accounts for 50.6% of the mean annual inflow to the Lake, whichrnincludes the direct rainfall over the lake and river inflow from the lake catchment.