It has long been proposed that various features within and beyond the confines of the Greenlandic settlement of Garðar, in modern Igaliku, reflect a medieval irrigation system with interconnected channels and cascading dams associated with Norse colonization and agriculture. These have rarely been investigated archaeologically or sedimentologically. After reviewing available evidence and the confusion surrounding terminology, this paper reports on excavations across three supposed irrigation channels. The lithostratigraphies of sediments located behind some of the proposed dams are also described and discussed. Although one of the excavated channels demonstrates convincing evidence for having been constructed (in part at least, through the presence of a vertical cut and the emplacement of flanking turf embankments), two of the channels are revealed as natural topographic features. It seems that if these were integrated into the Norse irrigation network then this was done without any further requirement for their modification or artificial enhancement. Deposits behind the dams were found to be shallow (~0.5 m deep) but contained sedimentary evidence for the former presence of standing water or waterlogged ground in the form of lake muds and peats. At one location (designated as Dam IX), radiocarbon dating of a stratigraphic change from lake mud to peat—indicating succession from open water to more terrestrial conditions—has been dated to cal. AD 1420–1620 [2s] and may reflect the reservoir falling into disuse following site abandonment. While doubt is thrown on the existence of one dam identified by previous investigators, two possible new dam/reservoir features are presented.