A portable breakwater system for use in a body of water includes first and second support members adapted to be positioned on the floor of the body of water and a curtain attached between the first and second support members. The first and second support members allow the curtain to freely rise in response to a wave in the body of water so as to attenuate the wave. Each support member includes a base plate and a frame assembly extending upwardly from the base plate. The base plates can be anchored to the water floor with one or more weights. The frame assemblies include pivoting or telescoping sections that permit the curtain to rise in response to a wave. Alternatively, the curtain can be attached to pre-existing underwater structure, such as the support members of a dock located in the body of water. In this case, the curtain is attached to the support members via attachment sleeves that are slidingly mounted on the support members.