In a suction dredger comprising a vessel having a hold for the storage of dredged material, means for emptying said hold, a suction conduit with a suction head, a suction-pressure pump in the suction conduit having a pressure conduit debouching within the hold, said vessel having its own power and control means, collecting means positionable at the side of the vessel and adapted to intersect the water surface and having means for sucking up oil floating upon the water surface and collected by the collecting means, said vessel having tanks for the storage of the sucked up oil-water mixture;
- the improvement in which said tanks are comprised by the open hold of the vessel normally serving for the storage of dredged material and the means for sucking up oil have said pressure conduit debouching into said hold, each said collecting means comprising a sweeping arm connected to a connection arm which is connected swingably about at least a horizontal axis to a carrier attached to the edge of the deck, said connection arm extending rearwardly from said carrier and having its rear end carrying the sweeping arm via a universal joint.