Chronic renal failure (CRF) associated with elevated dietary cadmium (Cd) among farming communities in the irrigated agricultural area under the River Mahaweli diversion scheme has reached a significantly higher level of 9,000 patients. Cadmium, derived from contaminated phosphate fertiliser, in irrigation water finds its way into reservoirs, and finally to food, causing chronic renal failure among consumers. During the present study, the authors collected and analysed water samples from the River Mahaweli and its tributaries in the upper catchment for total cadmium contamination of river water and the possible source of cadmium. Except a single tributary (Ulapane Stream, 3.9 íg Cd/l), all other tested tributaries carried more than 5 íg Cd/l, the maximum concentration level accepted to be safe in drinking water. Seven medium-sized streams carrying surface runoff from tea estates had 5.1-10 íg Cd/l. Twenty larger tributaries (Oya), where the catchment is under vegetable and home garden cultivation, carried 10.1-15 íg Cd/l. Nine other major tributaries had extremely high levels of Cd, reaching 20 íg Cd/l. Using geographical information system (GIS), the area in the catchment of each tributary was studied. The specific cropping system in each watershed was detected. The total cadmium loading from each crop area was estimated using the rates and types of phosphate fertiliser used by the respective farmers and the amount of cadmium contained in each type of fertiliser used. Eppawala rock phosphate (ERP), which is mostly used in tea estates, caused least pollution. The amount of cadmium in tributaries had a significant positive correlation with the cadmium loading of the cropping system. Dimbula Tea Estate Stream had the lowest Cd loading (495.9g/ha/yr), compared with vegetable-growing areas in Uma Oya catchment with 50,852.5 g Cd/ha/yr. Kendall’s ô rank correlation value of total Cd loading from the catchment by phosphate fertiliser used in all crops in the catchment to the Cd content in the tributaries was +0.48. This indicated a major contribution by the cropping system in the upper catchment area of River Mahaweli to the eventual Cd pollution of river water. Low soil pH (4.5-5.2), higher organic matter content (2-3%), and 18-20 cmol/kg cation exchange capacity (CEC) in upcountry soil have a cumulative effect in the easy release of Cd from soil with the heavy surface runoff in the upcountry wet zone. In view of the existing water conveyance system from upcountry to reservoirs in North Central Province (NCP) through diversion of River Mahaweli, in addition to their own nonpoint pollution by triple superphosphate fertiliser (TSP), this demands a change in overall upper catchment management to minimise Cd pollution through agriculture inputs to prevent CRF due to elevated dietary cadmium among NCP farmers.