The East River, locally known as Dongjiang, is the major source of potable water supply for Hong Kong. Because of the rapid economic development in the basin, concerns have been raised regarding the water quality in the river. In this study, total nitrogen (TN) export from the basin in 1998 is estimated for various sources based on a simple correlative approach utilizing measured concentrations in the river, together with some mass balance constraints based on socio-economic data. A modeling tool, HSP-F, is used for discharge calculation. The export coefficients for four land-use classes are calibrated and compared with literature. It is found that municipal input together with the contribution from farm animals are the major sources of nitrogen in the basin. A total load of 113, 000 t N/a has been estimated, giving an average specific export coefficient of 41.5 kg/ha/a, of which 68% are from non-point sources from the urban land-use and 17% from farm animals. The spatial distribution of nitrogen provenance is highly uneven and is concentrated in the downstream areas near Huizhou, Dongguan and Shenzhen. Copyright © 2009 Hong Kong Geographical Association.