In one aspect the invention provides a fluid treatment apparatus for treating contaminated fluid. The apparatus comprises a container having base member and a peripheral containment wall and defining a total interior volume. The apparatus further comprises at least one container inlet to receive said contaminated fluid, at least one container outlet to discharge water separated from said contaminated fluid, a separation region suitable to receive said contaminated fluid, to allow separation of said contaminated fluids into less dense contaminants, water and denser contaminants, and to store said denser contaminants as a sediment layer on the base member. The apparatus further comprises a water collection region suitable to receive water from the separation region and direct said water to said at least one container outlet, and an oil collection region, suitable to receive less dense contaminants from the separation region.