A submersible, water circulation system for enclosed tanks such as used by municipalities, fire districts, and industries. The system includes a driving unit having a shell extending along an axis with a pump supported within the shell. The shell has at least one inlet and at least one outlet and is positionable on the floor of the tank with the outlet facing upwardly. The upwardly facing outlet is preferably a thin, upwardly facing, elongated slot and creates a thin, substantially planar discharge of water therethrough that is directed upwardly toward the surface of the body of water. The substantially planar discharge presents a very large surface area for its volume and induces water adjacent the outside of the shell of the driving unit to move upwardly with it toward the surface of the body of water.