Floating hydroelectric power plant intended to be partially submerged in a watercourse, comprising: - a flotation member comprising at least two hulls extended according to the direction of the current, parallel and symmetrical to one another with respect to a first vertical plane and coupled by a framework; - a fully submerged channel having a rectangular internal cross section, convergent then divergent in the direction of the current, of length /, and having a vertical plane of symmetry coincident with the first plane, said channel being formed by an upper fairing and a lower fairing, at least horizontal ± 10% at the level of the throat of the channel, and by a pair of lateral fairings; - a vertical connecting structure, symmetrical with respect to the first plane, which connects the channel to the flotation member and which is fixed to the framework and to the upper fairing; - a turbine engine comprising two adjacent and contra-rotating turbines, housed in the channel, each equipped with N blades, N being equal to or greater than 2, said blades, moved by lift forces, sweeping a cylinder during a rotation movement of the turbines about axes of rotation ( Γ,Γ') each situated in a second vertical plane (A') that passes through the throat of the channel, cutting the first plane perpendicularly along a central vertical axis ( Δ), each turbine being connected by a first pivot link to a first casing within the upper fairing in order to guide the turbine in rotation and by a second pivot link to a second casing within the lower fairing in order to drive a generator housed in the second casing, one of the two generators being adjusted to rotate at an optimal rotation speed as a function of the speed of the incident current and the other generator being adjusted to rotate at the same speed of rotation; and - a holding device suitable for withstanding the drag force to which the floating hydroelectric power plant is subjected when it is partially submerged in the watercourse, comprising a mooring line under tension, inclined with respect to a horizontal plane by an angle of inclination ( α), comprising an upper part and a lower part, the lower part being situated upstream according to the direction of the current with respect to the upper part, the upper part being composed of an element fixed at a downstream end at a first point situated on a vertical column within the channel the axis of which coincides with said central axis (Δ), at equal distance, ± 10%, from the upper and lower fairings and the lower part being composed of one or more elements, each being fixed at their upstream end on an anchoring system intended to be firmly fixed to the bed or the banks of the watercourse, each element of the mooring line comprising a cable, a rope, a rod and/or a chain. - a flotation member comprising at least two hulls extended according to the direction of the current, parallel and symmetrical to one another with respect to a first vertical plane and coupled by a framework; - a fully submerged channel having a rectangular internal cross section, convergent then divergent in the direction of the current, of length /, and having a vertical plane of symmetry coincident with the first plane, said channel being formed by an upper fairing and a lower fairing, at least horizontal ± 10% at the level of the throat of the channel, and by a pair of lateral fairings; - a vertical connecting structure, symmetrical with respect to the first plane, which connects the channel to the flotation member and which is fixed to the framework and to the upper fairing; - a turbine engine comprising two adjacent and contra-rotating turbines, housed in the channel, each equipped with N blades, N being equal to or greater than 2, said blades, moved by lift forces, sweeping a cylinder during a rotation movement of the turbines about axes of rotation ( Γ,Γ') each situated in a second vertical plane (A') that passes through the throat of the channel, cutting the first plane perpendicularly along a central vertical axis ( Δ), each turbine being connected by a first pivot link to a first casing within the upper fairing in order to guide the turbine in rotation and by a second pivot link to a second casing within the lower fairing in order to drive a generator housed in the second casing, one of the two generators being adjusted to rotate at an optimal rotation speed as a function of the speed of the incident current and the other generator being adjusted to rotate at the same speed of rotation; and - a holding device suitable for withstanding the drag force to which the floating hydroelectric power plant is subjected when it is partially submerged in the watercourse, comprising a mooring line under tension, inclined with respect to a horizontal plane by an angle of inclination ( α), comprising an upper part and a lower part, the lower part being situated upstream according to the direction of the current with respect to the upper part, the upper part being composed of an element fixed at a downstream end at a first point situated on a vertical column within the channel the axis of which coincides with said central axis (Δ), at equal distance, ± 10%, from the upper and lower fairings and the lower part being composed of one or more elements, each being fixed at their upstream end on an anchoring system intended to be firmly fixed to the bed or the banks of the watercourse, each element of the mooring line comprising a cable, a rope, a rod and/or a chain.