A dissolved gas flotation apparatus (10) comprises: - a flotation tank(18) having an upstream contact zone separated by a baffle (9) from a downstream clarification zone; - one or more pressure reduction nozzles (28) arranged to discharge into the contact zone of the flotation tank (18); - a flow-straightening arrangement including two or more plate-like barriers (104) in the contact zone of the flotation tank (18), wherein: each barrier (104) has walls, the walls of the barriers (104) together defining flow paths in a desired direction; and each barrier (104) provides a barrier to horizontal flow perpendicular to the desired flow direction.