Groundwater flow is examined in a glacial geologic environment thought to be typical of the Clay Belt of northern Ontario. The geologic framework comprises two eskerine sand bodies separated and partially covered by an extensive plain of lacustrine clay, all underlain by discontinuous till resting on fractured crystalline bedrock. The groundwater flow medium is characterized by large hydraulic conductivity variations ranging over at least four orders of magnitude. Consequently, two distinctive types of groundwater environment are recognized: the esker environments consisting of elongated linear bodies of very permeable sand and gravel, and the clay plain environment characterized by a clay-over-till layered medium of relatively low permeability.Piezometric head measurements are interpreted with the aid of a numerical model of the potential field, obtained as a solution to the differential equation of steady-state groundwater flow. Three types of groundwater flow systems are distinguished: local flow systems associated with the topographically high eskers, local flow systems of limited lateral extent centered around the entrenched valleys in the clay plain, and regional flow systems with recharge in the flat interstream clay plain areas extending into the bedrock.