Analysis of stable oxygen isotope (δ¹⁸O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of spatio-temporal δ¹⁸O variations in glacier rivers, we have examined three glacierized catchments in Greenland with different areas, glacier hydrology and thermal regimes. At Mittivakkat Gletscher River, a small river draining a local temperate glacier in southeast Greenland, diurnal oscillations in δ¹⁸O occur with a three-hour time lag to the diurnal oscillations in runoff. Throughout the peak flow season the δ¹⁸O composition is controlled by the proportion between snowmelt and ice melt with episodic inputs of rainwater and occasional storage and release of a specific water component due to changes in the subglacial drainage system. At Kuannersuit Glacier River on the island Qeqertarsuaq, the δ¹⁸O characteristics were examined after the major 1995-1998 glacier surge event. Despite large variations in the δ¹⁸O values of glacier ice on the newly formed glacier tongue, there were no diurnal oscillations in the bulk meltwater emanating from the glacier in the post-surge years 2000-2001. In 2002 there were indications of diurnal oscillations, and in 2003 there were large diurnal fluctuations in δ¹⁸O. At Watson River, a large catchment at the western margin of the Greenland Ice Sheet, the spatial distribution of δ¹⁸O in the river system was applied to fingerprint the relative runoff contributions from sub-catchments. Spot sampling indicates that during the early melt season most of the river water (64-73 %) derived from the Qinnguata Kuussua tributary, whereas the water flow on 23 July 2009 was dominated by bulk meltwater from the Akuliarusiarsuup Kuua tributary (where 7 and 67 % originated from the Russell Glacier and Leverett Glacier sub-catchments, respectively). A comparison of the δ¹⁸O compositions from glacial river water in Greenland shows distinct differences between water draining local glaciers (between -17.4 and -13.7 ‰), large ice caps (between -23.0 and -17.8 ‰) and the Greenland Ice Sheet (between -29.9 and -23.2 ‰).