Apparatus for generating electricity using tidal, wave or current flow in a body of water, comprising: an arrangement of first (10) and second (11) pipes, each first pipe (10) being provided with a series of holes (12a, 12b, 13a, 13b) spaced along its length, and the first pipes being arranged relative to the second pipes such that a venturi is defined between the walls of adjacent first and second pipes near the holes; a flow conduit having an inlet and an outlet; an impeller located in the flow conduit; and a generator connected to the impeller; wherein water from the body can enter the flow conduit via the inlet, and the first pipes are connected to the outlet of the flow conduit such that flow of water past the arrangement of first (10) and second (11) pipes causes the first pipes (10) to act as venturi pumps inducing flow from the inside of the first pipes through the holes (12, 13) so as to draw water through the flow conduit and drive the impeller.