Urbanization dramatically alters stream water quality and ecosystem function, including through alterations to organic matter inputs and transformations. Such alterations have been linked to urban landcover and imperviousness, but watershed processes and water management not represented in traditional landscape metrics can override that relationship. We asked: what landscape characteristics are associated with organic matter sources in urban streams? We measured dissolved organic carbon (DOC) concentrations and fluorescence across four seasons at 100 sites within the Jordan River network in Salt Lake City, Utah, US. We hypothesized that water infrastructure like canals and wastewater treatment plants would shape the quantity and quality of organic matter in the stream network, and that the drivers of water quality would vary seasonally. DOC varied seasonally with the highest concentrations occurring during the summer sampling period. Organic matter quality varied primarily along a gradient from humic to autochthonous. Through stepwise regression, we found autochthonous organic matter was primarily associated with the number of road-stream crossings and forest landcover during the fall and winter seasons, but in the spring and summer we found the income of residents to be strongly associated. Sources and transformations of urban organic matter are shaped by different watershed processes depending on seasonal climate and water management. Predicting organic matter quantity and quality was most successful when incorporating landscape characteristics unique to Salt Lake City rather than relying on national data sets alone. Our findings emphasize the dynamic relationship between the landscape and water quality, and the importance of local context when managing ecosystems.