Provided is a novel flow control system that includes multiple modifier columns for positioning across a waterway. Bottom ends of the columns are attached to a bottom track extension, for example, at the bottom of the waterway. The columns are sufficiently light so that the buoyancy force pushes their top ends towards the surface forming a “curtain-like” structure that provides resistance to the water flow. Spacing between the columns and other characteristics may be used to adjust this resistance. The columns may be repositioned along the track to change the spacing and/or to form an open pass. The columns are sufficiently robust and may swivel with respect to their bottom support such that their upper portions contact passing vessels. The system may be used to control flow through energy extracting devices or be a part of flood control systems.