Hydropower plants provide an asset over other renewables of production flexibility. Away from the turbine design point; detrimental off-load instabilities may compromise the power generation consistency. During part-load operations; the draft tube swirl strongly couples the precessing motion of the vortex rope with the propagation of low-frequency pressure pulsations, further excessive fluid-structure interactions and power swings. To counteract that excitation; different attempts have been devised to dampen local pressure amplitude and detune the instability frequency against the natural system resonance. This article reviews strengths and weaknesses of those remedial attempts applied in the draft tube. They have been categorized as (1) Structural passive methods of shape optimization, J-grooves, stabilizer fins, adjustable diaphragm, baffles, runner cone extension and flow deflectors; (2) Fluidic active techniques of air and water supply and; (3) the hybrid flow control of different approaches. Frequent problems for their optimized effectiveness are: proper dimensions against flow intrusion, vibration and efficiency; location and configuration; performance deterioration of pressure recovery and cavitation; supply conditions of ancillary fluids; hydraulic/head losses; and the activation energy requirement. Future CFD-assisted considerations mainly call for rare hybrid remedy, as no single method can adequately address all instability problems from the draft tube. (C) 2020 Elsevier Ltd. All rights reserved.Y