Low-frequency waves generated by a submerged curvilinear sill due to bichromatic wave groups with and without an opposing current are studied experimentally in a laboratory flume.Second-order wave maker theory is used in the generation of the primary waves and the spurious long waves are significantly suppressed.The generation of harmonics,wave blocking of the short waves and especially the penetration of long waves through the “blocking point” are observed.The evolution of long waves before and after the blocking point is described in detail.