Natural rivers, including their riparian zones, belong to the most diverse, dynamic, and complex ecosystems on the world’s continents, and they play key roles in the regulation and maintenance of biodiversity in the landscape (Dynesius and Nilsson, 1994). Hydropower has a major macro-economic impact since it supplies more than 50% of national electricity production in 65 countries (Koch, 2002). Today about two-thirds of the fresh water flowing to the oceans is obstructed by approximately 40,000 large dams and more than 900,000 smaller ones (Petts, 1984; McCully, 1996). Hydropower regulation of river bodies was for a long time considered to be an environmentally friendly source of energy (Renöfält et al., 2009). However, damming of rivers has later been recognized as one of the most dramatic anthropogenic impacts on the natural environment (Petts, 1984). A comparison between one regulated and one pristine river with similar features, both located in Northern Sweden, has been conducted (Collomp 2001). The Luleå River comprises 15 reservoirs and has been regulated for almost a century (72 % of the annual river runoff can be stored in its reservoirs) (Dynesius and Nilsson, 1994). The Kalix River, the last major unregulated river in Europe, is used as a reference for geochemical conditions in a pristine river.Water storage in reservoirs affects seasonal water discharge, water temperature, conductivity and concentrations of nutrients, dissolved oxygen, organic matter and metals. Spring peaks are truncated and postponed and average base flow is higher than that under pristine conditions. Due to increased sedimentation in the reservoirs, the transport of Fe, Si, Al, Mn, DOC, P and N has decreased (Drugge, 2003). The aim of the outlined study is to increase knowledge regarding the effect of river regulation on riparian groundwater geochemistry by:a) analysing river water measurements with respect to river-groundwater exchangeb) measuring riparian groundwater quality at one site in each of the two riversIn both rivers, sampling sites were chosen approximately 100 km upstream of the river mouth. The geological settings and climatic conditions are similar in the two chosen areas, with precipitation rates of about 400 mm/year. In the regulated Luleå River, frequent water level fluctuations cause continuous mixing of river water and groundwater. Land use in both areas is equally non-intensive, and hydropower exploitation of the Luleå River is the only notable difference in land use in the two areas. The monitoring program at each site includes installation of 2-3 groundwater wells, with data loggers continuously recording groundwater levels, temperature, pH, conductivity, DO and ORP. Water samples will be taken weekly or bi-weekly for metal and nutrient analyses, and the hydraulic conductivities at the sites will be determined in soil samples. Expected outcome: Improved knowledge regarding river regulation impact on riparian groundwater, based on comparison of a one-year cycle of seasonal variations in groundwater flow and quality in a heavily regulated and a nearby pristine river.