: Agricultural and residential activities are key non‐point sources of nitrogen pollution in urban‐rural fringe areas. A GIS‐based watershed approach was used to compare land use indicators (septic system and animal unit densities), to streamwater nitrate‐N in the Salmon River near Vancouver, B.C., Canada. The density of septic systems was used as an indicator of residential development while animal unit density was used as an indicator of the intensity of agricultural activity. Nitrate‐nitrogen (nitrate‐N) concentrations as high as 7.1 mg·L−1 were found in the mid‐portion of the watershed during the summer months, when streamflow is low and groundwater comprises a large proportion of water in the stream. The major aquifer supplying water to the midsection of the watershed is contaminated with nitrate‐N. A comparison of the relationships between septic system and animal unit density and nitrate‐N in the upstream to downstream direction provided evidence that both residential and agricultural activities contribute to elevated nitrate‐N in the Salmon River mainstem. In contrast, only septic system density corresponded to the pattern of streamwater nitrate‐N in Coghlan Creek, the main tributary to the Salmon River.

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