A flow slowing boom for slowing the speed of a buoyant fluid floating on moving water having a direction of water movement and a water surface includes a support structure for positioning at the surface of a body of water across the direction of water movement; an anchoring structure for anchoring the support structure relative to the moving water; a skirt structure; and a pivot structure interconnecting the support structure and the skirt structure so that the skirt structure is pivotably suspended from the support structure and moving water pivots the skirt structure out of a suspended vertical orientation to any of a range of angles beyond vertical including horizontal, thereby constraining buoyant fluid to flow across the skirt structure to slow the speed of the fluid and thus to permit the fluid to buoy toward the water surface for containment. A boom system and method are also provided.