The invention relates to an underwater turbine for use under water, that may comprise fish, for instance intended for placement under water in the sea, such that electricity can be generated by tidal currents, the underwater turbine comprising a screw with a front side and a rear side, wherein water is forced from the front side to the rear side in use and comprising a hub and at least two blades extending from said hub, wherein a tubular housing having a free rear side end is provided around the blades, wherein the blades are substantially helical-shaped, wherein the blades extend from the hub in the direction of the outer circumference and the front side of the screw in a helical shape, wherein the blades taper off to a point in the outer circumference of the screw at the front side resulting in sickle-shaped blades with free ends near the outer circumference at the front side of the screw, the blades extending in a continuous manner from the front side end to the free rear side end of the tubular housing, wherein the effective surface area of the blades increases continuously from the front side toward the place where they are mounted on the hub, so that the fish in the water are mostly guided along the hub without being touched by the blades, the water with the fish leaving the free rear side end of the tubular housing unguided.
