Human and industrial activity generates wastewaters, which, treated or not, enter adjacent fluvial ecosystems. In the best scenario, treated wastewaters still act as a point source of nutrients, emerging pollutants and microorganisms to receiving streams. Depending on the dilution capacity of the receiving stream, these point sources can significantly alter the structure (e.g., microbial community composition, biomass standing stock) and function (e.g., metabolism, nutrient cycling, greenhouse gas emissions) of receiving streams, with downstream consequences for water quality, aquatic life, and human health. Yet, the in-stream imprint downstream urban point sources may vary along the fluvial continuum depending on the chemical composition of the wastewater effluent and its relative contribution to receiving stream flow. In this context, we may expect a decreasing imprint as the receiving streams become larger (i.e., higher Strahler order). This presentation is intended to introduce the context and objectives of this special session, and to illustrate it with current examples from streams in the Mediterranean region. We will use the empirical experience from our group to: a) show the effect of wastewater treatment plant inputs as sources of nutrients, emergent pollutants and microbial pathogens to streams, b) discuss how the hydromorphological conditions and bioreactive capacity of receiving streams can buffer these inputs, and c) discuss how these effects and responses can vary across river networks.