Urbanization impacts aquatic ecosystems in a heterogenous manner, and the driving factors fluctuate both spatially and temporally. One area which is still not well understood is how urbanization impacts the bioavailability of dissolved organic carbon. Bioavailable dissolved organic carbon (BDOC) is a measure of how readily organic carbon is utilized by heterotrophic microorganisms and is dependent on the size and molecular composition of the dissolved organic carbon. We hypothesized that BDOC would peak in the dry season and decrease through the wet season, and that urban factors would significantly influence BDOC. Seasonal surface water sampling occurred in eight watersheds within the Portland, OR metropolitan area between July 2023 and May 2024. The samples were filtered, inoculated with mixed unfiltered water, then incubated in the dark at 20°C for 28 days. Temporal and spatial difference were evaluated using mixed-model ANOVA and the relationship between BDOC and urbanization was modeled using stepwise regressions per season, and redundancy analysis (RDA) for the whole year. BDOC levels changed significantly seasonally as well as between watersheds. Four watersheds saw BDOC decrease from summer peaks through Winter and then increase again in Spring. The other four trended differently, some increasing in Fall and Winter, or decreasing in the Spring. The regressions modeled that correlation with BDOC fluctuates between urban characteristics during the dry season and in-stream processes during the wet season. BDOC was consistently associated with stream metabolism, and the direction of the seasonal correlations suggest that BDOC reflects both autotrophic production and microbial uptake. In the dry season, BDOC shared significant relationships with urban factors (Summer R2 0.84), and in the wet season BDOC was associated with in-stream processes (Spring R2 0.60). The RDA identified relationships between the BDOC and factors such as infrastructure age, urban density, canopy cover, and precipitation. The model also revealed that, while urban factors do influence BDOC, seasonal fluctuations govern these urban stream systems, further evidenced by the variable correlations identified by the regression models. These results contribute to further understanding heterogeneous urban impacts coupled with seasonality and how these factors influence the freshwater carbon cycle.