Aquatic Ecosystem Services were contracted by the Kerio Valley Development Authority and CMC Kenya to undertake the specialist ichthyofaunal studies on the Arror and Kimwarer rivers in the Kerio Valley. The studies are being undertaken to inform the EIA for multipurpose dams which are being proposed for development on the upper escarpment on both tributaries of the Kerio River. AES conducted a wet season field survey in collaboration with scientists from the National Museums of Kenya during August 2017. A low flow survey is planned for January 2018. This study is the first assessment of the ichthyofauna within the two tributaries of the Kerio River and the information will be used to inform the design, implementation and management of the dam projects.