The flow caused by a line source discharging into a stagnant, linearly density stratified reservoir was studied in a tank. The flow enters the reservoir as a horizontal line jet but immediately passes through an internal hydraulic jump and forms a slowly moving wedge of fluid mixed into the injection by the jump. The inflow also induces a series of layers of flow in alternating directions above and below the entering layer. The mixed layer was made visible by mixing blue dye into the supply fluid. The length, thickness, and tip speed of the mixed layer were measured as a function of time, and an empirical scaling relationship was derived. The results may be used to predict the extent of mixed layers which might occur during the pumping phase in a jump-storage reservoir.