This study aims to assess the effects of land cover change on water quality in River Ruiru watershed by integrating remotely sensed data, Geographic Information System and the Soil and Water Assessment Tool (SWAT) model. Landsat 5 TM 1984 and OLI-TIRS 2017 images were categorized into seven land cover classes following a technique. The study findings indicate that built-up, annual crops and perennial crops areas increased by 1.83%, 15.05% and 10.90% respectively between 1984 and 2017. On the contrary, grassland, shrubland and forestland declined by 6.21%, 11.92% and 10.66% respectively. Consequently, findings from the study indicate that nitrates in the surface runoff (NO3SURQ), nitrates in lateral runoff (NO3LATQ), organic nitrogen (N.ORG) and organic phosphorus (P.ORG) increased from 0.05kgN/ha/yr, 0.06kgN/ha/yr, 5.77kgN/ha/yr and 0.87kgP/ha/yr respectively in 1984 to 1.47kgN/ha/yr, 0.19kgN/ha/yr, 70.60kgN/ha/yr and 8.86kgP/ha/year respectively 2017. This could be attributed to the expansion of agricultural areas both annual and perennial crops, increased use of inorganic fertilizers rich in nitrates and phosphorus, increased surface runoff from the cultivated lands and loss of natural land cover. As such, remedial actions to address the effects of land cover change on water quality both by the national and county governments are required. These may include agricultural best management practices and integrated water resources management.

GIS, Integrated Water Resources Management, Nitrates, Organic Nitrogen, Organic Phosphorus, Remote sensing