A water circulation apparatus for desratifying a body of water such as in a lake or reservoir is disclosed. Broadly, the apparatus (1) comprises ducting in the form of a draft tube (2) having an upper end (3) positioned towards the surface of the body of water and a lower end (4) positioned towards the bottom of the body of water, and a pump assembly (5) for pumping water through the tube (2). Broadly, the pump assembly (5) comprises an impeller (20) having six to fourteen blades (21) having a diameter of 3 m-5 m driven by an electrical motor. Typically, the apparatus (1) also includes a support in the form of a platform (13) mounted on buoyancy elements (12). Water enters the draft tube (2) through the upper end thereof and is pumped outwardly through the tube (2) and out through the outlet spaced above the bottom of the body of water. The apparatus is used to pump water across a thermocline which acts as a barrier to normal convection flow so as to destratify the body of water and to resist the occurrence of a layer of deoxygenated water near the bottom of the body of water.