Watershed behaviour results from many processes, nested at different scales and that influence the hydrological linkages between landscape units. In the aim to delineate the skeleton processes controlling the contributions of different water sources through the Arctic summer, we instrumented the Apex River watershed with 27 flow monitoring and water sampling stations. Monitoring stations were installed on headwater tributaries (15) and on different reaches (12) along the main branches of the river. Salt gauging and cross-sectional gauging were used to monitor the flow on the headwater tributaries and main reaches respectively. All sites were equipped with pressure sensors-loggers monitoring the water level in the streams, in the aim the derive continuous rating-curve discharge measurements. Between June 19th and July 31st, site measurements (12) of the water temperature and electrical conductivity were conducted prior to each water sampling. Water samples were analyzed for pH and filter within 3-4 hours after the sampling. Filtered samples were kept refrigerated in ether scintillation or amber glass EPA vials until analysis in Mélissa Lafrenière’s laboratory in Kingston, Ontario. Natural tracers (Dissolved Organic Carbon, Total Dissolved Nitrogen, Oxygen and Hydrogen Isotopes) will be measured using a Shimadzu TOC-VCPH Analyzer and a Los Gatos Research (LGR) Liquid-Water Isotope Analyzer, to provide insights on the course of water flowing through our sampling sites.