Concentrators for recovering liquid pollutant floating on the surface of a sheet of water

A concentrator for the recovery of a water-immiscible liquid pollutant floating on the surface of a sheet of water, which comprises a duct of flexible material having an inlet orifice with a larger and a smaller dimension along mutually perpendicular axes for locating with its larger dimension substantially parallel to the surface of the sheet of water, the shape of the duct varying across its length such that at its end remote from the inlet orifice it has a section with a larger and a smaller dimension along mutually perpendicular axes, its larger dimension being in a plane substantially perpendicular to the surface of the sheet of water when the larger dimension of the inlet orifice is parallel to the surface of the sheet of water, a flexible grid connected across the inlet orifice so as to maintain a fixed geometry of said inlet orifice, at least one outlet orifice for the outflow of the liquid pollutant from the concentrator, a tubular coupling connected to the outlet orifice for the liquid pollutant for recovery of the pollutant therefrom by pumping, an upper transverse float extending the length of the inlet orifice, and at least one float extending the length of the duct, the cross-sectional area of said duct being substantially constant between the inlet and outlet orifices.