An apparatus for installing across a body of water such that there is a head drop from the upstream side to the downstream side of the apparatus for generating electricity using water flow in the body of water comprising: - an array of spaced apart pipes, each pipe defining an elongate flow passage and having an upstream side and an elongate downstream side, each pipe being provided with a series of holes spaced along at least part of its length and the elongate downstream side extending and tapering away from the upstream side, wherein the pipes are arranged side by side such that opposing walls of adjacent pipes define a venturi section and a first diffuser section extending downstream from the venturi section; - a flow conduit having an inlet and an outlet; - a turbine located in the flow conduit; and - a generator or hydraulic pump connected to the turbine; wherein the flow passages are connected to the outlet of the flow conduit such that a primary flow of water through the venturi sections causes a secondary flow of water to be drawn through the flow conduit and out via the holes with the resulting secondary flow of water driving the turbine, wherein the upstream side of each pipe extends and tapers away from the holes to form an elongate shape such that when the pipes are arranged side by side in an array, opposing walls of adjacent pipes define a second diffuser section extending upstream from the venturi section, wherein the holes are arranged so that the secondary flow joins the primary flow as it leaves the pipes through the holes, and wherein the pipes are arranged horizontally. - an array of spaced apart pipes, each pipe defining an elongate flow passage and having an upstream side and an elongate downstream side, each pipe being provided with a series of holes spaced along at least part of its length and the elongate downstream side extending and tapering away from the upstream side, wherein the pipes are arranged side by side such that opposing walls of adjacent pipes define a venturi section and a first diffuser section extending downstream from the venturi section; - a flow conduit having an inlet and an outlet; - a turbine located in the flow conduit; and - a generator or hydraulic pump connected to the turbine; wherein the flow passages are connected to the outlet of the flow conduit such that a primary flow of water through the venturi sections causes a secondary flow of water to be drawn through the flow conduit and out via the holes with the resulting secondary flow of water driving the turbine, wherein the upstream side of each pipe extends and tapers away from the holes to form an elongate shape such that when the pipes are arranged side by side in an array, opposing walls of adjacent pipes define a second diffuser section extending upstream from the venturi section, wherein the holes are arranged so that the secondary flow joins the primary flow as it leaves the pipes through the holes, and wherein the pipes are arranged horizontally. wherein the flow passages are connected to the outlet of the flow conduit such that a primary flow of water through the venturi sections causes a secondary flow of water to be drawn through the flow conduit and out via the holes with the resulting secondary flow of water driving the turbine, wherein the upstream side of each pipe extends and tapers away from the holes to form an elongate shape such that when the pipes are arranged side by side in an array, opposing walls of adjacent pipes define a second diffuser section extending upstream from the venturi section, wherein the holes are arranged so that the secondary flow joins the primary flow as it leaves the pipes through the holes, and wherein the pipes are arranged horizontally.