Potential Risks of Pesticide Application in Kenya: Case of Lake Naivasha Catchment Joel Onyango 1,4 , Norbert Kreuzinger 2 , Paul Yillia 2 , Nzula Kitaka 3 1 UNESCO-IHE Institute for Water Education, Westvest 7, 2611AX, Delft, The Netherlands (corresponding author, email j.onyango@unesco-ihe.org ) 2 Research Center for Water Quality Management, Institute for Water Quality, Resources and Waste Management, Technical University of Vienna, Karlsplatz 13/226, A-1040 Vienna, Austria (email: norbkreu@iwag.tuwien.ac.at ) 3 Department of Biological Sciences, Egerton University, P.O. Box 536 Egerton, Kenya (email: nkitaka@yahoo.com ) 4 ACTS – African Centre for Technology Studies, P.O. Box 45971 – 00100, Nairobi, Kenya Abstract This study focuses on the pesticides that are applied within Lake Naivasha catchment as gathered from farms and agricultural offices within the region. The study aims at providing a basis for monitoring pesticides residue contamination of the water bodies in Lake Naivasha catchment including L. Naivasha, and Rivers Malewa, Karati and Gilgil. This study answers the question of whether pesticides of international concern (“Dirty Dozen”) are still being used within the L. Naivasha catchment. Thirty two pesticide active ingredients were identified in the study including, insecticides (52%), fungicides (33%) or herbicides (15%). Some of the chemical types of pesticides identified were pyrethroids (19%), organochlorides (9%), organophosphates (9%), conazoles (6%) and dithiocarbamates (6%). Although majority of the pesticides identified were moderately hazardours (WHO Toxicity Class II), extremely hazardours to highly hazadours pesticides were also identified. The study concludes that there is continued use of pesticides of international concer, including the”dirty dozen” and regulation mechanisms need to be evaluated.