Tana River basin covers approximately 21 % of Kenya's total land area. The basin produces about 33.5 % of the country's surface water and 23.8 % of ground water that supports about seven million people. To assess metal and nutrient concentration of Tana River surface water, 57 and 53 water samples were collected in wet (May) and dry (August) seasons of 2018, respectively. Cadmium, chromium, nickel, lead, mercury, arsenic, manganese, zinc, copper, aluminum, boron, selenium, fluoride, chloride, total phosphorus and nitrate were analyzed. Water quality index (WQI) was used to classify water quality into four categories based on pollution level while hazard quotient (HQ) and hazard index (HI) were used to assess non-carcinogenic risk posed to human health since majority of people in the lower reach use Tana River water without any form of treatment. Multivariate statistical analysis was applied to deduce associations and identify pollution sources. Arsenic, cadmium, lead, nickel, selenium and mercury were not detected while manganese, chloride and aluminum were the principal pollutants in the two seasons. 26.3 % of all studied sites recorded HQ > 1 due to high Mn contamination. WQI was noted to be unreliable risk assessment tool since it did not correlate well with HQ and HI besides portraying all sampling sites as bearing suitable water for drinking. Tana River is at risk of eutrophication since total phosphorus concentration detected exceeded recommended threshold. Leached fertilizer from encroached riparian zone, fuel from leaking irrigation pumps and cleaning of motor bikes on water ways was the main source of anthropogenic pollution. Pollution processes and practices observed can be remedied to curb detrimental effects on human health.
