In this field study, we investigated how particulate organic matter (POM) and dissolved organic matter (DOM) quantity and its biochemical quality changed between lake inflow and outflow as well as within the oligotrophic, pre-alpine Lake Lunz, Austria, from 2013 to 2015. We tested the hypothesis that irrespective of seasons, stream recharging the lake contains predominantly recalcitrant POM (>1.2 m) and DOM (<0.2 m), whereas outflow lake water is composed of more labile, algae-derived organic matter. Samples were collected at a monthly basis from lake, inflow and outflow stream, and analysed for fatty acids as biochemical indicators of POM and optical indices and matrices for DOM quality. Results showed that precipitation and runoff significantly predicted the influx rate of POM (r = 0.72, R2=0.52, Sig. F<0.001) and DOC (r = 0.4, R2=0.16, Sig. F=0.04). Lake retained 58% of imported POM, but exported 3X, 8X, and 6X high bacterial fatty acids (BAFA), and algae-derived omega-3 and omega-6 PUFA, respectively, than the inflow. Long-chain SAFA (used as proxy for terrestrial organic matter) constituted 9% in inflow and 6% of total SAFA in the outflow. The optical characterization of DOM, depicted that the prevalence of allochthonous DOM in inflow and hypolimnion was significantly higher than in epilimnion and outflow (p<0.05). The HIX and BIX values also suggest that inflow was a predominant source of terrigenous organic matter, whereas the epilimnion and outflow indicated prevalence of high bacterial and algal derived DOM. In general, Lake Lunz exports on average 8X more labile POM (algae-derived) and DOM containing 21% less allochthonous and 35% more autochthonous OM than inflow. These results suggest that Lake Lunz is a biochemical upgrader within the fluvial network of this drainage basin and supplies highly labile and nutritional POM and DOM to consumers further downstream, irrespective of the season.