A mixing apparatus for mixing relatively low salinity fluid with relatively high salinity fluid comprisesa housing having an upper end and a lower end, a fluid inlet at or near the lower end, and a fluid outlet at or near the upper end, wherein the relatively high salinity fluid in use enters the housing through the fluid inlet and is discharged from the housing through the fluid outlet. A feed tube is provided and has a first end connectable to a source of relatively low salinity fluid and second end for introducing relatively low salinity fluid to the housing to mix the relatively high salinity fluid with the relatively low salinity fluid to form a fluid mixture. At least one power generator is associated with the housing, and is driven by the mixing of the relatively high salinity fluid with the relatively low salinity fluid.