NOVELTY - Two sets (65,66) of coaxial rotating blades (10,15) are arranged so that one cannot eclipse another. The blades are mounted adjacent to one another. One set is arranged upstream of the other set of blades. The other set is arranged for contra-rotation relative to the other set of blades. The blades are mounted on shafts (20,25) coupled to a rotor (45) and a stator (55) of an electrical generator (50). Each set of blade is operable to extract similar amounts of energy. Each set has a different number of blades to generate different reactive torque.    USE - For generating power from a tidal stream for an electrical generator.    ADVANTAGE - The multiple sets of turbine blades increase the efficiency of energy capture. The two contra-rotating sets of blades in close proximity lead to near zero reactive torque on the system. This allows greater flexibility in the design of the supporting structure and eliminates piling placed in the sea or river bed. The components are lighter and cheaper as they do not need the strength to withstand the high degree of reactive torque. The greater relative rotational speed of the rotor and stator enables up to 50 percent reduction in the number of machine electrical poles in comparison to a standard machine of the same rating. Lighter, simpler and more compact gearing mechanism is used or even no gearing at all, with the generator being directly driven. The swirl produced by the downstream blades are arranged to cancel out the swirl produced by the upstream blades. This reduces the environmental impact associated with scouring of the seabed by swirl. The relative motion of the contra-rotating rotors makes it hard for marine organisms to settle on them which lead to a reduction in bio-fouling of the blades.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for the generator.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a contra rotating turbine and generator unit with the generator housing cut away in cross section.    Rotating blades (10,15)    Shafts (20,25)    Rotor (45)    Electrical generator (50)    Stator (55)    Sets of blades (65,66)