Relict deltas of well-sorted and well-drained sands are among numerous strand-line deposits that mark the former shoreline positions of glacial Lake Iroquois in northern New York. In this study, ground penetrating radar (GPR) was used to image the subsurface architecture of four Late Pleistocene lacustrine deltas to provide information about their depositional environment. The surveyed deltas indicate two distinct glacial Lake Iroquois water levels, the Frontenac and Trenton water phases. A pulseEKKO 100 GPR unit and a 400 Vtransmitter, combined with 50 and 100 MHz antennas are used to provide a better understanding of the internal structures, delta thickness, and distinct facies units. Delta thickness varies generally from 10 to >20 m. High-resolution GPR profiles exhibit variable reflection continuity. Depositional patterns of four distinct radarfacies are described as being characteristic of foreset bed, braided channel, channel cut and fill, and lacustrine clay, in addition to fine-grained till deposits. Facies units reflect an environment of a braided delta in which high sediment volumes and unstable directions of deposition dominated. Larger boulders of nonriverine origin that are located within deltaic sediments are interpreted as dropstones. Waterlevels of glacial Lake Iroquois appear to be stable during the relatively short periods of delta formation. Deltas of glacial Lake Iroquois exhibit lobate morphology typical of a constructive environment.