Models based on stream tube geometry and geostrophy are used to describe the passage of a strong river through a long narrow (fjord-type) lake. Analysis is specifically applied to the entry of the Thompson River into Kamloops Lake, British Columbia. Lake-river interaction is considered in three stages of flow: a sinking plume stage during which the incoming river water sinks to a depth where its density matches that of the incoming river, a horizontal spreading stage during which the movement of river water is unconstrained by bottom and/or shoreline effects, and a shorebound stage during which the flow of river water downlake occurs principally in a balance between cross-stream pressure gradients and the Coriolis force. Exchanges of mass and momentum are parameterized by entrainment and friction coefficients evaluated from field data. Results of this study show, in general, that river-induced currents influence or even dominate circulation patterns within a fjord lake.