An undersea power generation apparatus (1) includes two turbines (3) mounted side by side at either side of a support strut of hydrofoil-shaped cross section, each turbine (3) having a set of turbine blades which counter rotate so as to cancel out the respective torque produced by each turbine. The apparatus (1) is pivotally interconnected at point (9) to a pair of mooring cables (7), which are releasably moored to the seabed (6). The turbines (3) are positively buoyant such that in zero current they point vertically upwards as denoted by (8). When the current flows in the direction shown by arrow A, the drag forces on turbines (3) and support strut cause the apparatus (1) to pivot about point (9) and pitch over into condition denoted by (10) and shown in broken lines.