A filtration system for a fuel system for a marine vessel engine. The system comprising: an inlet for fluid connection to a settling tank; an outlet for fluid connection to a service tank; and an arrangement of plural primary filtration devices The arrangement is fluidly connected between the inlet and outlet so that fuel flowing from the settling tank via the inlet to the service tank via the outlet passes through at least one of the primary filtration devices. The system is configured so that each respective primary filtration device operates, independently of each other primary filtration device in: a first mode, in which the fuel flows in a first direction through a filter of the respective primary filtration device to remove contaminants from the fuel, or a second mode, in which a fluid flows through the filter in a second direction, opposite the first direction, to dislodge the contaminants.