The urban stream syndrome describes the multiple changes that co-occur when a stream becomes urbanized, affecting flow, biogeochemistry, microbiota, and biodiversity. The multiple symptoms of the urban stream syndrome are attenuated as water flows downstream either by dilution or via active transformations by aquatic processes which are affected by flow conditions. We addressed the question of how a suite of changes caused by urbanization are transferred through an entire river network under both high and low flow conditions. We conducted synoptic surveys throughout the river network of the Tordera River watershed, Catalonia, Spain, during March (high flow) and July (low flow) 2025. We measured flow, specific conductance, pH, dissolved oxygen, temperature, cations, anions, inorganic and organic nutrients, organic carbon, greenhouse gases, microplastics, and microbial communities from headwaters of different land use through tributaries and mainstem, as well as inputs from wastewater treatment plants. We found that specific conductance, a conservative tracer, increased steadily along the Tordera continuum under both high and low flow conditions, consistent with increasing population and wastewater treatment plant effluent moving downstream. Surprisingly, overall specific conductance levels were only slightly higher under low flow compared to high flow indicating minimal dilution at high flows. Nitrate increased along the Tordera continuum similar to those for conductance during high flow, but during low flow, nitrate did not increase despite considerable wastewater and diffuse N sources. This result suggests that in stream processes are able to mitigate bioreactive compounds (e.g. nitrate) entering the river network under certain conditions, attenuating a portion of the urban stream syndrome from being expressed further downstream.